The reason I want to do this is because the blank pages reflect the exact layout of PDF documents (sequence, orientation, page size) that I have (I don't have the source for these original PDF). If I can put line numbers on these pages and export to PDF, it's just a simple matter of overlaying these numbered pages onto my final documents. You may say, why not use a PDF editor to do this - well it would be very slow for thousands of pages. Neither do I want to use OCR, as this is also very time consuming and can change formatting.

If I can just find a way to fill the blank pages with line breaks or paragraph breaks so they are no longer empty, then this would achieve everything I want. Maybe there is a way through find and replace? Or maybe a simple macro would do it?