Your two-sided print job needs to be an even number of pages so each new section starts on a right-hand page. The PDF is odd-numbered. You need a blank page inserted before a specific section.
Flint's edit tool supports blank page insertion.
Pick a position, click insert
Open edit PDF, drop the file. In the page panel, click between two pages where you want the blank inserted. Choose 'insert blank page'. A new blank page appears at that position. The PDF page count increases by one.
Choose size and orientation
Blank pages default to the surrounding pages' size and orientation. If your document is A4 portrait, the blank is A4 portrait. Override if needed: insert a blank A3 page in a document of A4 pages for a foldout placeholder.
Multiple blanks
Need a blank between every chapter? Insert one at a time at each chapter boundary. Or split into per-chapter files and merge back with blank cover pages between chapters — different approach for the same effect.
Use cases
Even-page padding for duplex printing. Notes pages between chapters. Reservation for a foldout or insert. Cover/divider pages for sections. PDF can hold blanks indefinitely with no quality issue — they're empty pages, not visual artifacts.
FAQ
Will the blank page print?
Yes, as a blank sheet. That's usually what you want for duplex padding.
Does it affect file size?
Negligibly. A blank page adds a tiny bit of metadata.
Can I add lined paper as a 'blank' page?
Use merge to insert a custom 'blank' (e.g. a lined-paper PDF) at the right position.
Will bookmarks remap?
Yes. Bookmarks for pages after the insertion point shift by one position.
Click between pages, insert. Add a blank page.