Hi louish70815980 ,
Would like to inform that You can apply as many signatures to a PDF file as you want with different signing credentials. If you have signing credentials for different people on the same computer these people definitely can apply their signatures on this computer. If you transfer a [possibly already signed] PDF to a different computer, you can sign this PDF with more signatures with the signing credentials that reside on that computer. All Acrobat needs to sign is a signing credential (certificate with a password key).
When you create a PDF you can pre-populate it with unsigned signature fields, which people will use to sign (this is a preferable workflow) or you can just graw a rectangle where you want a new signature to appear on a page and Acrobat will place the new signature there. Again, either way, you (or other people) can sign a PDF as many times as you wish.
Please refer to this article as well :- https://helpx.adobe.com/acrobat/using/digital-ids.html
Let me know if any issue persist.