I'm doing a miscellaneous quest called Collect Technical Documents for Proctor Quinlan but when I bring him some documents, he gives me some caps and tells me to go collect more technical documents. How do I complete this miscellaneous quest?

You don't. It's sort of a radiant quest that never ends, as upon starting it, technical documents spawn indefinitely throughout the Commonwealth. It's basically an endless means of making caps in the game, should you come across technical documents in your travels.

As mentioned, this never ends. You can keep finding more technical documents and turning them in for caps. Scribe Neriah on the Prydwen has a very similar quest finding viable blood samples for her research too. These aren't really 'quests.' It's just something to keep your eye out for while you're out doing quests.

They will be helpful when you need extra caps or quick EXP boost

"All right, we have enough information on pre-war tech, time to shut it down." said no BoS scribe ever.

Depending on when you get the tasks to find these items they might be obsolete. I choose to join the factions when I had explored and done all other quests than the faction/mainquest related quests and I already had like 50k caps so getting another 1000 caps was for me kind of un-neccessary.