If during upload, a file is converted/modified, it will yield a new SHA256sum (see #2327). If the same file is uploaded again, the conversion/modification will likely produce a completely new file with a different SHA256sum (because of timestamps in the generated PDF etc.). Therefore, even with skipDuplicates in metadata, certain duplicates cannot be prevented in the status quo.

The original SHA256sum is kept in the table filemeta. It should be used instead of the hashsum of the converted file.