diff --git a/Gemfile b/Gemfile
index 9337c4c..dca768b 100644
--- a/Gemfile
+++ b/Gemfile
@@ -3,5 +3,4 @@ source 'https://rubygems.org'
 # Specify your gem's dependencies in win32-certstore.gemspec
 gemspec
 
-gem 'rb-readline', '~> 0.5.3'
-gem 'pry'
+gem 'rb-readline'
diff --git a/lib/win32-certstore.rb b/lib/win32-certstore.rb
index 67e109a..c65bab7 100644
--- a/lib/win32-certstore.rb
+++ b/lib/win32-certstore.rb
@@ -1,5 +1,21 @@
 $LOAD_PATH.unshift File.expand_path('../../lib/win32', __FILE__)
+#
+# Author:: Nimisha Sharad (<nimisha.sharad@msystechnologies.com>)
+# Copyright:: Copyright (c) 2017 Chef Software, Inc.
+# License:: Apache License, Version 2.0
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
 
-require "store/crypto"
+require "mixin/crypto"
 require "certstore/certstore"
 require "win32-certstore/version"
diff --git a/lib/win32/certstore/certstore.rb b/lib/win32/certstore/certstore.rb
index d77d35a..ed84c3f 100644
--- a/lib/win32/certstore/certstore.rb
+++ b/lib/win32/certstore/certstore.rb
@@ -15,48 +15,59 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-require 'store/crypto'
-require 'store/assertions'
+require 'mixin/crypto'
+require 'mixin/assertions'
 require_relative 'store_base'
 
 module Win32
   class Certstore
-    include Win32::Store::Crypto
-    extend Win32::Store::Assertions
+    include Win32::Mixin::Crypto
+    extend Win32::Mixin::Assertions
     include Chef::Mixin::WideString
-    extend Win32::Certstore::StoreBase
+    include Win32::Certstore::StoreBase
 
-    attr_accessor :store_name
+    attr_reader :store_name
+
+    def initialize(store_name)
+      @certstore_handler = open(store_name)
+    end
 
     def self.open(store_name)
       validate_store(store_name)
-      @certstore_handle = self.new.send(:open, store_name)
       if block_given?
-        yield self
+        yield self.new(store_name)
       else
-        self
+        self.new(store_name)
       end
     end
 
-    def self.list
-      list = cert_list(@certstore_handle)
-      self.new.send(:close)
+    def list
+      list = cert_list(@certstore_handler)
+      close
       return list
     end
 
+    def add(cert_file_path)
+      add = cert_add(@certstore_handler, cert_file_path)
+      close
+      return add
+    end
+
     private
+    
+    attr_reader :certstore_handler
 
     def open(store_name)
-      certstore_handle = CertOpenSystemStoreW(nil, wstring(store_name))
-      unless certstore_handle
+      certstore_handler = CertOpenSystemStoreW(nil, wstring(store_name))
+      unless certstore_handler
         last_error = FFI::LastError.error
         raise Chef::Exceptions::Win32APIError, "Unable to open the Certificate Store `#{store_name}` with error: #{last_error}."
       end
-      certstore_handle
+      certstore_handler
     end
 
     def close
-      closed = CertCloseStore(@certstore_handle, CERT_CLOSE_STORE_FORCE_FLAG)
+      closed = CertCloseStore(@certstore_handler, CERT_CLOSE_STORE_FORCE_FLAG)
       unless closed
         last_error = FFI::LastError.error
         raise Chef::Exceptions::Win32APIError, "Unable to close the Certificate Store with error: #{last_error}."
diff --git a/lib/win32/certstore/store_base.rb b/lib/win32/certstore/store_base.rb
index c5653d9..02ac78d 100644
--- a/lib/win32/certstore/store_base.rb
+++ b/lib/win32/certstore/store_base.rb
@@ -15,48 +15,79 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-require 'store/crypto'
+require 'mixin/crypto'
+require 'openssl'
 
 module Win32
   class Certstore
     module StoreBase
-      include Win32::Store::Crypto
+      include Win32::Mixin::Crypto
+      include Win32::Mixin::Assertions
       include Chef::Mixin::WideString
+      include Chef::Mixin::ShellOut
 
-      def cert_list(certstore_handle)
+      def cert_list(store_handler)
         cert_name = FFI::MemoryPointer.new(2, 128)
         cert_list = []
         begin
-          while (pCertContext = CertEnumCertificatesInStore(certstore_handle, pCertContext) and not pCertContext.null? ) do
+          while (pCertContext = CertEnumCertificatesInStore(store_handler, pCertContext) and not pCertContext.null? ) do
             if (CertGetNameStringW(pCertContext, CERT_NAME_FRIENDLY_DISPLAY_TYPE, CERT_NAME_ISSUER_FLAG, nil, cert_name, 1024))
               cert_list << cert_name.read_wstring
             end
           end
           CertFreeCertificateContext(pCertContext)
         rescue Exception => e
-          lookup_error
+          lookup_error("list")
         end
         cert_list.to_json
       end
+      
+      def cert_add(store_handler, cert_file_path)
+        validate_certificate(cert_file_path)
+        file_content = read_certificate_content(cert_file_path)
+        pointer_cert = FFI::MemoryPointer.from_string(file_content)
+        cert_length = file_content.bytesize
+        begin
+          if (CertAddEncodedCertificateToStore(store_handler, X509_ASN_ENCODING, pointer_cert, cert_length, 2, nil))
+            "Added certificate #{File.basename(cert_file_path)} successfully"
+          else
+            lookup_error
+          end
+        rescue Exception => e
+          lookup_error("add")
+        end
+      end
 
       private
 
-      def lookup_error
+      def lookup_error(failed_operation = nil)
         last_error = FFI::LastError.error
         case last_error
         when 1223
-          raise Chef::Exceptions::Win32APIError, "The operation was canceled by the user. "
+          raise Chef::Exceptions::Win32APIError, "The operation was canceled by the user."
         when -2146885628
           raise Chef::Exceptions::Win32APIError, "Cannot find object or property."
         when -2146885629
-          raise Chef::Exceptions::Win32APIError, "An error occurred while reading or writing to a file. "
+          raise Chef::Exceptions::Win32APIError, "An error occurred while reading or writing to a file."
         when -2146881269
           raise Chef::Exceptions::Win32APIError, "ASN1 bad tag value met. -- Is the certificate in DER format?"
         when -2146881278
-          raise Chef::Exceptions::Win32APIError, "ASN1 unexpected end of data.  "
+          raise Chef::Exceptions::Win32APIError, "ASN1 unexpected end of data."
         else
-          raise Chef::Exceptions::Win32APIError, "Unable to load certificate with error: #{last_error}."
+          raise Chef::Exceptions::Win32APIError, "Unable to #{failed_operation} certificate with error: #{last_error}."
+        end
+      end
+
+      # This is a single public certificate in X509 DER format.
+      # If your certificate has a header and footer line like "---- BEGIN CERTIFICATE ----" then it is in PEM format, not DER format.
+      # A certificate can be converted with `openssl x509 -in example.crt -out example.der -outform DER`
+      def read_certificate_content(cert_path)
+        unless (File.extname(cert_path) == ".der")
+          temp_file = shell_out("powershell.exe -Command $env:temp").stdout.strip.concat("\\TempCert.der")
+          shell_out("powershell.exe -Command openssl x509 -in #{cert_path} -outform DER -out #{temp_file}")
+          cert_path = temp_file
         end
+        File.read("#{cert_path}")
       end
 
     end
diff --git a/lib/win32/store/assertions.rb b/lib/win32/mixin/assertions.rb
similarity index 78%
rename from lib/win32/store/assertions.rb
rename to lib/win32/mixin/assertions.rb
index 5209618..3662951 100644
--- a/lib/win32/store/assertions.rb
+++ b/lib/win32/mixin/assertions.rb
@@ -15,12 +15,19 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-module Win32::Store::Assertions
+module Win32::Mixin::Assertions
 
   # Validate certificate store name
   def validate_store(store_name)
     unless valid_store_name.include?(store_name&.upcase)
-      raise ArgumentError, "Invalid Certificate Store. Valid certificate store name are: #{valid_store_name}"
+      raise ArgumentError, "Invalid Certificate Store."
+    end
+  end
+
+  # Validate certificate type
+  def validate_certificate(cert_file_path)
+    unless (!cert_file_path.nil? && File.extname(cert_file_path) =~ /.cer|.crt|.pfx|.der/ )
+      raise ArgumentError, "Invalid Certificate format."
     end
   end
 
diff --git a/lib/win32/store/crypto.rb b/lib/win32/mixin/crypto.rb
similarity index 82%
rename from lib/win32/store/crypto.rb
rename to lib/win32/mixin/crypto.rb
index 0ffc74a..477ebbf 100644
--- a/lib/win32/store/crypto.rb
+++ b/lib/win32/mixin/crypto.rb
@@ -22,7 +22,7 @@
 require 'mixlib/shellout'
 
 module Win32
-  module Store
+  module Mixin
     module Crypto
       extend Chef::ReservedNames::Win32::API
       extend FFI::Library
@@ -69,11 +69,15 @@ module Crypto
       BYTE                                                = FFI::TypeDefs[:pointer]
 
       class CERT_CONTEXT < FFI::Struct
-        layout :hCertStore,  :HANDLE,
-        :dwCertEncodingType, :DWORD,
-        :pbCertEncoded,      :PWSTR,
-        :cbCertEncoded,      :DWORD,
-        :pCertInfo,          :pointer
+        layout :cbElement,   :DWORD,
+        :pbElement,          :pointer
+        def initialize(str = nil)
+          super(nil)
+          if str
+            self[:pbElement] = FFI::MemoryPointer.from_string(str)
+            self[:cbElement] = str.bytesize
+          end
+        end
       end
 
       ###############################################################################
@@ -94,6 +98,12 @@ class CERT_CONTEXT < FFI::Struct
       safe_attach_function :CertEnumCertificateContextProperties, [PCCERT_CONTEXT, :DWORD], :DWORD
       # Clean up
       safe_attach_function :CertFreeCertificateContext, [PCCERT_CONTEXT], :BOOL
+      # Add certificate file in certificate store.
+      safe_attach_function :CertAddSerializedElementToStore, [HCERTSTORE, :pointer, :DWORD, :DWORD, :DWORD, :DWORD, :LMSTR, :LPVOID], :BOOL
+      # Add certification to certification store - Ref: https://msdn.microsoft.com/en-us/library/windows/desktop/aa376015(v=vs.85).aspx
+      safe_attach_function :CertAddEncodedCertificateToStore, [HCERTSTORE, :DWORD, :PWSTR, :DWORD, :INT_PTR, PCCERT_CONTEXT], :BOOL
+
+      safe_attach_function :CertSerializeCertificateStoreElement, [PCCERT_CONTEXT, :DWORD, :pointer, :DWORD], :BOOL
     end
   end
 end
diff --git a/spec/win32/unit/assets/example-cert.der b/spec/win32/unit/assets/example-cert.der
new file mode 100644
index 0000000..87e554c
Binary files /dev/null and b/spec/win32/unit/assets/example-cert.der differ
diff --git a/spec/win32/unit/certstore/certstore_spec.rb b/spec/win32/unit/certstore/certstore_spec.rb
index e551ba5..b0c8977 100644
--- a/spec/win32/unit/certstore/certstore_spec.rb
+++ b/spec/win32/unit/certstore/certstore_spec.rb
@@ -21,26 +21,27 @@
 describe Win32::Certstore do
 
   let (:certstore) { Win32::Certstore }
+  let (:certbase) { Win32::Certstore::StoreBase }
   
   describe "#list" do
     context "When passing empty certificate store name" do
       let (:store_name) { "" }
-      it "Raise ArgumentError" do
-        expect { certstore.open(store_name) }.to raise_error(ArgumentError)
+      it "raises ArgumentError" do
+        expect { certstore.open(store_name) }.to raise_error("Invalid Certificate Store.")
       end
     end
 
     context "When passing invalid certificate store name" do
       let (:store_name) { "Chef" }
-      it "Raise ArgumentError" do
-        expect { certstore.open(store_name) }.to raise_error(ArgumentError)
+      it "raises ArgumentError" do
+        expect { certstore.open(store_name) }.to raise_error("Invalid Certificate Store.")
       end
     end
 
     context "When passing empty certificate store name" do
       let (:store_name) { nil }
-      it "Raise ArgumentError" do
-        expect { certstore.open(store_name) }.to raise_error(ArgumentError)
+      it "raises ArgumentError" do
+        expect { certstore.open(store_name) }.to raise_error("Invalid Certificate Store.")
       end
     end
 
@@ -48,9 +49,9 @@
       let (:store_name) { "root" }
       let (:root_certificate_name) { "Microsoft Root Certificate Authority"}
       before(:each) do
-        allow_any_instance_of(Win32::Certstore::StoreBase).to receive(:cert_list).and_return([root_certificate_name])
+        allow_any_instance_of(certbase).to receive(:cert_list).and_return([root_certificate_name])
       end
-      it "return certificate list" do
+      it "returns certificate list" do
         store = certstore.open(store_name)
         certificate_list = store.list
         expect(certificate_list.size).to eql(1)
@@ -58,15 +59,53 @@
       end
     end
 
-    context "When passing valid certificate store name" do
+    context "When adding invalid certificate" do
       let (:store_name) { "root" }
-      before(:each) do
-        allow_any_instance_of(Win32::Certstore::StoreBase).to receive(:cert_list).and_return([])
+      let (:cert_file_path) { '.\win32\unit\assets\test.cer' }
+      it "returns no certificate list" do
+        allow(certbase).to receive(:CertAddEncodedCertificateToStore).and_return(false)
+        store = certstore.open(store_name)
+        expect { store.add(cert_file_path) }.to raise_error(Chef::Exceptions::Win32APIError)
+      end
+    end
+
+    context "When adding certificate failed with FFI::LastError" do
+      let (:store_name) { "root" }
+      let (:cert_file_path) { '.\win32\unit\assets\test.cer' }
+      
+      it "returns 'The operation was canceled by the user'" do
+        allow(certbase).to receive(:CertAddEncodedCertificateToStore).and_return(false)
+        allow(FFI::LastError).to receive(:error).and_return(1223)
+        store = certstore.open(store_name)
+        expect { store.add(cert_file_path) }.to raise_error("The operation was canceled by the user.")
       end
-      it "return no certificate list" do
+
+      it "returns 'Cannot find object or property'" do
+        allow(certbase).to receive(:CertAddEncodedCertificateToStore).and_return(false)
+        allow(FFI::LastError).to receive(:error).and_return(-2146885628)
         store = certstore.open(store_name)
-        certificate_list = store.list
-        expect(certificate_list.size).to eql(0)
+        expect { store.add(cert_file_path) }.to raise_error("Cannot find object or property.")
+      end
+
+      it "returns 'An error occurred while reading or writing to a file'" do
+        allow(certbase).to receive(:CertAddEncodedCertificateToStore).and_return(false)
+        allow(FFI::LastError).to receive(:error).and_return(-2146885629)
+        store = certstore.open(store_name)
+        expect { store.add(cert_file_path) }.to raise_error("An error occurred while reading or writing to a file.")
+      end
+
+      it "returns 'ASN1 bad tag value met. -- Is the certificate in DER format?'" do
+        allow(certbase).to receive(:CertAddEncodedCertificateToStore).and_return(false)
+        allow(FFI::LastError).to receive(:error).and_return(-2146881269)
+        store = certstore.open(store_name)
+        expect { store.add(cert_file_path) }.to raise_error("ASN1 bad tag value met. -- Is the certificate in DER format?")
+      end
+
+      it "returns 'ASN1 unexpected end of data'" do
+        allow(certbase).to receive(:CertAddEncodedCertificateToStore).and_return(false)
+        allow(FFI::LastError).to receive(:error).and_return(-2146881278)
+        store = certstore.open(store_name)
+        expect { store.add(cert_file_path) }.to raise_error("ASN1 unexpected end of data.")
       end
     end
   end
diff --git a/spec/win32/unit/store/assertions_spec.rb b/spec/win32/unit/store/assertions_spec.rb
index aa5a85a..f12bb76 100644
--- a/spec/win32/unit/store/assertions_spec.rb
+++ b/spec/win32/unit/store/assertions_spec.rb
@@ -18,10 +18,10 @@
 
 require 'spec_helper'
 
-describe Win32::Store::Assertions do
+describe Win32::Mixin::Assertions do
 
   class Store
-    include Win32::Store::Assertions
+    include Win32::Mixin::Assertions
   end
 
   let (:certstore) { Store.new }
@@ -29,30 +29,60 @@ class Store
   describe "#validate_store" do
     context "When passing empty certificate store name" do
       let (:store_name) { "" }
-      it "Raise ArgumentError" do
-        expect { certstore.validate_store(store_name) }.to raise_error(ArgumentError)
+      it "raises ArgumentError" do
+        expect { certstore.validate_store(store_name) }.to raise_error("Invalid Certificate Store.")
       end
     end
 
     context "When passing invalid certificate store name" do
       let (:store_name) { "Chef" }
-      it "Raise ArgumentError" do
-        expect { certstore.validate_store(store_name) }.to raise_error(ArgumentError)
+      it "raises ArgumentError" do
+        expect { certstore.validate_store(store_name) }.to raise_error("Invalid Certificate Store.")
       end
     end
 
     context "When passing empty certificate store name" do
       let (:store_name) { nil }
-      it "Raise ArgumentError" do
-        expect { certstore.validate_store(store_name) }.to raise_error(ArgumentError)
+      it "raises ArgumentError" do
+        expect { certstore.validate_store(store_name) }.to raise_error("Invalid Certificate Store.")
       end
     end
 
     context "When passing valid certificate store name" do
       let (:store_name) { "root" }
-      it "Not Raise ArgumentError" do
+      it "does not raise ArgumentError" do
         expect { certstore.validate_store(store_name) }.not_to raise_error(ArgumentError)
       end
     end
   end
+
+  describe "#validate_certificate" do
+    context "When not passing certificate file" do
+      let (:cert_file_path) { "" }
+      it "raises ArgumentError" do
+        expect { certstore.validate_certificate(cert_file_path) }.to raise_error("Invalid Certificate format.")
+      end
+    end
+
+    context "When passing invalid certificate" do
+      let (:cert_file_path) { "Chef" }
+      it "raises ArgumentError" do
+        expect { certstore.validate_certificate(cert_file_path) }.to raise_error("Invalid Certificate format.")
+      end
+    end
+
+    context "When passing nil" do
+      let (:cert_file_path) { nil }
+      it "raises ArgumentError" do
+        expect { certstore.validate_certificate(cert_file_path) }.to raise_error("Invalid Certificate format.")
+      end
+    end
+
+    context "When passing valid certificate file" do
+      let (:cert_file_path) { '.\win32\unit\assets\test.der' }
+      it "does not raise ArgumentError" do
+        expect { certstore.validate_certificate(cert_file_path) }.not_to raise_error(ArgumentError)
+      end
+    end
+  end
 end