I was going to suggest a form rule to track the date the file attachment changed, but there's actually a documented bug that would prevent that "QBE002156: 'When Attachment type field changed (and record saved)' always triggers." Unfortunately I'm not aware of another method that would automatically track that change. You could however have a manually entered date field next to the file attachment and train your users to update it when they update the file attachment. Not 100% reliable but can hopefully get you the information you need.
Something went wrong with my pdf reader. I wanna convert pdf into text first. Any suggestion will be appreciated. Thanks in advance. http://www.pqscan.com/pdf-to-text/ How about the abovementioned one?