"Bad CPU type in executable" when running pdftk
As it says on https://www.pdflabs.com/tools/pdftk-server/, PDFtk Server is for &quot;Mac OS X 10.6 (Snow Leopard), 10.7 (Lion) and 10.8 (Mountain Lion)&quot;. The package only contains a 32bit binary which won't run on Catalina or Big Sur.
You may be able to install directly from source (see further down on the same page), or you reach out to the developers and ask for an update.