Hey Erin,
If you want to update an existing pdf follow these steps:
-Locate the pdf in design studio
-With the pdf selected, click the
"Replace Image or File" button.
-Browse and select the new document, click "
Replace" and you're good to go!
This will keep the same link (just change the file the link directs a user to), so any past emails should show your updated PDF.
Hope this helps!