Invoice pdf file via IDR grows from less than 1 MB to more than 10 MB - Approval email won't attach

Summary:

Some (not all, but enough) invoice pdf files processed through IDR go from original file size that is significantly less than 1 MB to more than 10 MB when invoice is created in Fusion and pdf invoice uploaded.

The increased attachment size poses a problem with invoice approval workflow emails as the limit per attachment for workflow email task attachment is 10 MB — so the IDR created invoice pdf (> 10MB) is not getting attached to the request-for-approval email. The email does include the attachment link, but that doesn't help in our case since majority of our approvers are approve-by-email-only users and do not approve by UI.