NEVER MIND - I fixed it by just rebooting DT. I’m leaving this message just in case anyone else has the same problem.
Usually, I can open pdfs from a database, annotate them, save, and then I’m able to open them again from the database.
Sometimes, however, I’ll make an annotation in the open pdf, try to save it, but DT says there is not enough data for an image (or something like that), then when I try to reopen the pdf I get “There was an error opening this document. There was an error reading this document (14)”. If memory serves, rebooting the computer fixed the problem sometimes but it doesn’t seem to be fixing things now.
I can still use the document in DT, and the previous links I created in RT documents still work . . . I just can’t open it to make new annotations on the PDF.
If it makes a difference, I’m running 10.13 6 on a Macbook Air and I’m running 2.11.3 in DT