Add PDF unlocking code

[nonprofittechy]

When I tried with this PDF: adr100.pdf

it didn't normalize the names. It looks like the form is "locked" from editing with no password. We should try automatically unlocking PDFs where it's possible or at least include a simple function that people can use for unlocking.

[nonprofittechy]

@colarusso, you do unlocking in your batch processing workflow: is that using something in Acrobat?

[nonprofittechy]

This seems to imply that just using pikepdf.open is enough: https://stackoverflow.com/questions/28192977/how-to-unlock-a-secured-read-protected-pdf-in-python