Thanks for the related topic, but not the same question.
On Windows, it exists tools (acrobat reader, foxit reader, …) which is able to open a signed PDF document and add both visible and invisible signature.
The visible signature, is only for information, and if document is printed.
The invisible signature is done by a certificate (in my case a smart card) to prove your identity.
With the invisible signature, when you open the PDF, you will see a message : “This document is numerically signed and the signature is valid” or something similar. And you are able to view who signed with which certification autority.
If I create a document or if I open a non signed document, I’m able to first
- add a visible signature (insert → signature line) => draw a rectangle, LO access my smart card request me to the pin code and show me my certificate. Choose the one to sign and add the visible signature on the document like the one produced by acrobat reader on Windows. Except that the date format is shorter on LO
if I export as PDF the document, without adding other information, and open it with Okular for example, there is no digital signature, only an information with acrobat logo
So to really sign the document, I have two options:
- In the export to pdf window, ‘digital signatures’ tab choose the certificate to use
or
- File → digital signatures → digital signatures
in the new window, sign the document, LO then export the document.
Problem: when you open an already digitally signed document, and try to add the “signatures line”, LO considers (I think it’s normal) that the document was modified and suppress the original signatures. So exporting the document will only kept my signature. I loose all other previous signature except the visible one’s. But the visible signature is just a “drawing”!
Parallel with windows: with acrobat reader or foxit reader, you are able to sign an already signed document. When you sign, you have both visible and invisible (certificate) signature
