How to flatten a PDF
1. Drop one PDF. Pictures and audio are refused here. 2. Leave “Bake form fields” when the text should stay selectable. Pick “Redraw pages as images” when a highlight, a stamp or a filled box must become pixels. 3. Press “Flatten PDF” and open the download.
Field mode draws each field’s value onto the page with pdf-lib and removes the form, so a reader cannot edit the boxes. Image mode paints each page with PDF.js, including the appearances of annotations, and builds a new PDF of those pictures.
Fields and annotations are not the same choice
Bake form fields keeps sentences you could already select, and it adds the field text as page content. Comments that are not fields stay as annotations. Use this when you filled a form and still want to search the words.
Redraw pages as images is the one that bakes what you see, including marks drawn on top. The new file has no form and the words are not selectable. It is the right download when the next step is print or a tool that ignores annotations.
What this does not do
A password-protected PDF must be unlocked first. Flatten does not compress, crop or sign. A file with no fields and no marks still downloads: field mode copies the pages, image mode redraws them.
How to check the flattened PDF
1. Open the download and try to click a field. It should not accept typing. 2. Try to select a sentence. Field mode still lets you. Image mode does not. 3. If a highlight disappeared, run again in image mode so the mark is painted into the page.
Field mode is the smaller, searchable file. Image mode is the picture of what you saw, including stamps. Unlock a password-protected PDF first. Nothing is uploaded.