I print some of my articles and catalog them in binders. In Bookends, I have changed one of the User fields to be Location - this tells me which binder, and which sleeve, such as K13.
I'm contemplating a switch from Bookends to Papers - is there a way to import these fields?
Sorry, this is not an answer to your question, but if you want to switch reference manager, then now is not a good time to switch to Papers. I really enjoyed using Papers 3, but since it has been bought by Readcube its future is not just uncertain, there is no future for Papers 3. It is also currently riddled with bugs and it is not actively maintained. It is really sad, especially for paying customers, but not the first time that a great product is being scrapped after it has been taken over. I hear other people actually making the move from Papers 3 to Bookends, which I am also considering.
That's the impression I'm starting to get. I had a (perhaps unfounded) belief that Papers was cool because they sponsored the PhD Movie. Maybe they were.
I was a bit miffed about Bookends latest upgrade for $40. Sounds like it might be a good investment after all.