Update Adobe Acrobat XI.
I will try to update ...
I also read:
"Certificate signing in Reader requires enablement in Acrobat XI Pro"
--> I have Standard Edition
Can somebody verify?
I don't use the Standard Edition.
Acrobat Reader 11.0.07 and later allows the user to sign without PDFs being Reader-extended. You are just one version behind.
Indeed ... i updated the AdobeReader to 11.0.14 and it works fine