A lot of countries don’t stamp a visa in your passport, but issue you a separate travel document that is surrender when you leave the country. Pakistan wasn’t one of those, but some countries which are a bit sensitive and maybe want to reassure visitors that their stay won’t be disclosed to folks that need not know, used these separate visas. One that I know did this was the Soviet Union, and I believe it possible that Israel also issues a separate travel document.
Cuba does the same if you ask.
Cuba does the same if you ask.