Adobe Acrobat or Adobe Acrobat Reader is required for the sign pro plug-in for Adobe Acrobat

When trying to capture a signature in Acrobat Reader an error message appears saying that the sign pro PDF plug-in is required even though it has been installed.

The most likely explanation of this error is that the sign pro plug-in for Adobe Acrobat is currently only available for 32-bit Adobe Acrobat.
The only remedy is to install a 32-bit version of Acrobat.
Please note that this is the current situation as of Jan 17th 2022 but in future it is possible that a 64-bit version of the plug-in will be developed.