You will have to first add a digital signature field to the document, which you can do with the doc.addField method: http://livedocs.adobe.com/acrobat_sdk/9.1/Acrobat9_1_HTMLHelp/JS_API_AcroJS.88.435.html
The script can be xecuted in a batch sequence, so you can easily process your collection of documents.
Thank you for the rapid response.
But i have no idea where to start....
Is there no finished program or macro which is easy to use??
I'm not aware of any. The documentation I directed you to includes some sample code. The script would first have to create the digital signature field somewhere on a page of the PDF and then sign it, using the signatureSign method. It has a lot of options, so it is difficult to give an example that is tailored to you needs. But the sample code should get you started.
I have the same problem to solve, and not too much knowledge on scripting.
This link appears to make a reasonable start; now if you can help "package" this as a working example, I guess users like me could take it forward from there...