So far, spotlight indexing of Papers’ keywords is not possible (while being planned for a future release according to an email that I received today from one author). In the meantime, here is a workaround.
1. Export the whole Papers database as tmp.csv
2. Cut down the database to the necessary two columns: filename und tags. This can be done manually by loading the while file into Excel and extracting only column 39=path and column 7=keywords.
If you feel comfortable with the terminal issue
cat ‘tmp.csv’ | awk -F”;” ‘{print $39 “;” $7}’ >ExportPapers.csv
3. Finally, use the following applescript for tagging (after adjusting all paths)
|wj_Papers.txt|