The pdfToolbox plugin for Acrobat can be easily removed by deleting the pdfToolbox9.acroplugin package in the callas software subfolder in the Plugins directory for Acrobat, under Mac.

Acrobat DC

Please note that as of Acrobat DC, Adobe has changed the folder in which it stores third-party plugins:
/Library/Application Support/Adobe/Acrobat/DC/Plug-ins/callas software 

Acrobat XI and older

For Acrobat XI and older, meanwhile, the plugin can be found in the following folder:
/Applications/Adobe Acrobat XI Pro/Adobe Acrobat Pro.app/Contents/Plug-ins/callas software

On Windows, the plugin can be found in the subfolder of the plugin directory for the current Acrobat version:
Acrobat\plug_ins\callas software

The folders and files contained within can be identified by their name, e.g. “pdfToolbox 8”, “pdfToolbox 9”.

Delete them to remove the plugin.