Digital signature is too complex for the average Joe, i.e. me
You need to make this easier and less quirky. I'm using a mac and have downloaded acrobat pro for windows and mac. It's taken me ages and youtube videos to create a digital signature and on a blank pdf I can add it. But when sent a pdf that already contains digital signatures it won't let me sign. In the end I used Mac Preview. This obliterated the original signatures but at least I could sign and send it back for resignature by others. The whole exercise is very unpleasant and very very annoying.
Admincdas (Admin, Adobe) commented
Acrobat allows multiple digital signatures on a document unless a pdf is locked after signing or the document is password protected and only filling of signature field is allowed.
Please open the doc in Acrobat. CTRL+D and go to Security Tab to check for the document properties.The Document restrictions summary will tell you the changes that are allowed.
In general, we can sign document multiple times using Certificates Tool