Questions about using Filecoin for document storage.

[tjaa26]

I am brand new to this technology, so please forgive my ignorance.

I seek 'immutable' file storage and I am unclear based on the website what service filecoin actually provides.

Is filecoin just a cloud storage service?
Does it guarantee file immutability?
Is there risk of file tampering, hacking, or deletion? Or, once uploaded, is a file essentially permanent?
Is it a one-time fee to upload a file, or a regular subscription fee to maintain files?
Can uploaded files be seen by anybody? Is there an option to make uploaded files publicly visible?
If I upload a large pdf, can anybody view it and can I be certain that nobody can tamper with or delete it?
Is there a limit to file sizes?

Thank you.