Create a digital signature: Do you mean a signature field, or a profile?
The former is done using the Add New Field tools in Prepare Form mode. The latter can be done via Edit - Preferences - Signatures - Identities & Trusted Certificates. Click on Add ID to create a new one, or to import one from a file. In the same window you can also export an existing signature profile from your old version to a PFX file, and then import it in the new version.
Thank you so much for your solutions. my previous Acrobat 10 pro has my digital signature on my old laptop, now i have a new laptop, so i need a way to transfer the signature from Acrobat 10 pro to Acrobat Pro 2020 ver 20. the exact menu location of these different version may be different, i guess. I will follow your steps try export profile from acrobat 10 and import to acrobat 2020, will do it next week and update here again.