Flatten PDF

How to flatten a PDF

1. Drop a PDF file on the drop zone, or click it to choose one. The tool counts what it finds under Found in this PDF: form fields, comments and drawings, sticky notes, and other annotations.
2. Under What to flatten, tick the items to lock: Form fields, Comments and drawings and, if you want, Sticky notes.
3. Click Flatten PDF, then Download. The file is named after the original, for example application_flat.pdf.

What flattening does

A PDF page has two layers. The page content is the text, images and vector graphics that make up the document itself. On top of it, a PDF can carry annotations: interactive objects such as form fields, highlights, comments, stamps and links. Every PDF reader lets you edit, move or delete annotations, and a filled form can be changed by anyone who opens it.

Flattening copies the visible appearance of each annotation into the page content and removes the annotation. The page looks exactly the same, but the values of a form can no longer be changed, and a reviewer’s highlights can no longer be deleted by accident. It’s the usual last step before you send a filled form, archive a contract or share a document that was annotated during a review.

What this tool can flatten, and what it keeps

This tool uses pdf-lib and follows the PDF specification: each annotation’s normal appearance stream is drawn at the exact position and size of the annotation, with its opacity.

• Form fields: text fields, check boxes, radio buttons, drop-down lists, list boxes and buttons. If a field has no appearance yet, or if the form asks readers to rebuild appearances, the tool first regenerates it with pdf-lib in Helvetica. The form itself (and any XFA copy of it) is then removed from the file.
• Comments and drawings: highlights, underlines, strike-outs, squiggly lines, text boxes (free text), rectangles, ellipses, lines, polygons, pen (ink) drawings, stamps, insertion marks and watermark annotations.
• Sticky notes: optional. The note icon is drawn on the page and the pop-up text is removed, because a flat page has nowhere to show it.

Some annotations are always kept: links stay clickable, and file attachments, sound and video are not converted. Redaction marks are not applied. Flattening a redaction annotation would only paint a box over text that is still in the file, so they are left alone; use a real redaction tool to remove sensitive content.

pdf-lib can create appearances for form fields but not for other annotations. An annotation saved without an appearance (rare, but some older editors do it) can’t be flattened: the tool leaves it in place and tells you how many were kept. Hidden annotations are removed.

Limits

• XFA-only forms (dynamic forms made with Adobe LiveCycle or AEM Designer) don’t store their fields as regular PDF fields. The tool reports them and can’t flatten them.
• Regenerated field appearances use Helvetica, which only writes Western European characters. A field containing, say, Cyrillic or Chinese keeps its last saved appearance.
• Flattening rewrites the file, so an existing digital signature stops validating. Flatten before signing, not after.
• Password-protected PDFs must be unlocked first.