[Frank Cox]

If one was intending to add a different field to every entry then doing it with a spreadsheet would indeed be simpler and definitely be the way to go.

But if you want to add exactly the same field to every entry (such as "genres=Country", for example) then the only way to do that is also with a spreadsheet.

I'm thinking that it would be nice to have a data entry screen along with the pdf bookmark import that says "everything set here gets added to each of these entries as they are imported."