Mac: The document “filename.pdf” could not be exported as filename.pdf

The error “The document “filename.pdf” could not be exported as filename.pdf” started appearing in Safari on attempting to save PDFs from the browser.

The problem appears to be update-related: apparently a recent Acrobat update left an old file in the plugins directory that needs to be deleted.

To fix, go to: 

Macintosh HD/Library/Internet-Plug-Ins/

and drag Adobe PDF Viewer.plugin or any other items that have the letters PDF in the name to the trash.

Quit and restart Safari then test downloading a PDF before emptying the trash.