[math-fun] Best way to handle large number of pdf files?

Ever since it started in 2007 I've been using PAPERS ( https://en.wikipedia.org/wiki/Papers_(software) ) to manage pdf files on my Mac. But lately it has gotten very slow to respond, maybe because of the large number of pdf files I have. It often takes a minute to respond. I know there are newer programs (Mendeley, Benubird, Zotero), but even if they are faster at dealing with a large library of files, there would still be the problem of moving the files over from PAPERS. Anyone have any advice? I'm running Papers3 Version 3.4.20 (579) on an iMac running OS 10.13.6.