multiple copies of same file

I created a database with about 900 files from several sources, mostly PDFs. In quite a few cases, the same file was imported from more than one place so the database has multiple copies of the same file. These do not show up in the Duplicates smart folder. How can I get rid of the unwanted copies?

If DEVONthink doesn’t mark them as duplicates, then it’s likely that the files are at least slightly different in some way. However, one possibility is to select all files and to run the script Scripts > Data > Find & Remove Similar Contents… afterwards.

Thanks for your reply.
The differences must have been quite subtle. They didn’t show up in the Finder’s Get Info window.
The script was not useful because it also picked up non-duplicate files. Turned out to be best simply to remove the duplicates by hand.