PDFtk hanging on MacOS Sierra
Use this version:
https://www.pdflabs.com/tools/pdftk-the-pdf-toolkit/pdftk_server-2.02-mac_osx-10.11-setup.pkg
Although it’s prepared for El Capitan (10.11), it also works on Big Sur (11), Catalina (10.15), Mojave (10.14), High Sierra (10.13), and Sierra (10.12).