I don't know about Acrobat 8, but in Acrobat 9 you can remove a digital ID by selecting: Advanced > Security Settings > Digital IDs > [select ID] > Remove ID
There should be something similar for Acrobat 8 somewhere.
Thanks George for the help, I managed to create my own ID using your
approach, Advanced > Security Settings > Digital IDs > add ID, but when I
signed it with the PDF of my signature, it is showed as my name in Typing
such as "XXX YY", instead of the handwritten form. I managed to use the
same PDF of my signature (signed and converted to PDF) last week when I
used the Pro 9, how can I attach my signature the same way in handwritten
form instead of being convered to "XXX YY" and appears "digitally signed"
You can customize the appearance of your digital signatures by doing: Acrobat > Preferences > Security > Digital Signatures > Appearance
This is what it is on Acrobat 9, I don't know about Acrobat 8.
You can create as many different appearances as you want and can include a graphic/image of your handwritten signature. When you apply a signature, you should see where it allows you to select an appearance to use.
Great, George, it works!! Many thanks!