Flatten PDF

It converts everything that is "live" in the document into static, baked-in page content. Form fields that were fillable (text boxes, checkboxes, radio buttons, dropdowns) become normal text and graphics — you can still see the filled values, but no one can edit them. Annotations like sticky notes, highlights, freehand drawings, and stamps get drawn directly onto the page. Layers (Optional Content Groups) are merged into a single visible layer. After flattening, the PDF looks identical when viewed, but it behaves like a printed page — what you see is all there is, and none of it can be modified through the normal Acrobat UI.

Two reasons. For printing: many printer drivers ignore form-field values that have not been "committed" — you fill in your name, send to print, and the printout shows blank fields. Flattening renders the values onto the page so they always print. For archiving: standards like PDF/A explicitly forbid interactive elements because they cannot guarantee the document will display the same way in 30 years (the form-rendering JavaScript may not run anymore). Flattening turns the file into a self-contained snapshot — same visual content, no dependencies on a working form engine.

No. Flattening is a one-way operation: once form fields are converted to static content, the field definitions are removed from the PDF's AcroForm dictionary and cannot be reconstructed. This is by design — a flattened PDF should not have any editable surface left. Always keep a copy of the original (unflattened) PDF if you might need to edit it again later. Because this tool never modifies the file on your disk and only produces a new flattened PDF as the download, your source remains intact unless you manually overwrite it.

Be careful here. Digital signatures in PDFs are technically a special kind of form field — and flattening will visually preserve the signature appearance (the visible "Signed by..." stamp) but break the cryptographic validation. The signature certificate is tied to the unchanged bytes of the original PDF; once you flatten, the bytes change and any signature checker will report the file as modified after signing. If the PDF is legally signed and you need to keep that validation intact, do not flatten it. If you only need a visual record of the signed document for printing or archiving, flattening is fine.

They target different kinds of "live" content. Flatten Forms applies to interactive form fields — text inputs, checkboxes, radio buttons — and converts their current values into static text on the page. Remove Annotations applies to mark-up overlays — sticky notes, highlights, freehand drawings, comments, link rectangles — and either bakes their visible appearance into the page or strips them out entirely. You can do either or both. The most common use is "flatten forms + remove annotations" before sending a finished document for signing or archival, to ensure no one can edit the values or strip your comments.

Sometimes, modestly. Removing the AcroForm dictionary, JavaScript actions, and annotation objects frees up some bytes, especially in heavily-annotated PDFs. But the static rendered content (text, images, the visual appearance stream of each annotation) is now drawn permanently onto the page, which adds content. Net effect is usually a small size change in either direction — flattening is not a compression operation. If you want a smaller file, follow up with Compress PDF, which downsamples images and removes orphan objects from the now-flattened document.