Flatten PDF

A regular PDF separates content into layers:

• Page content — the printed text and images.
• Form fields — interactive boxes the user fills in (AcroForm or XFA).
• Annotations — highlights, comments, freehand drawings, sticky notes.
• Digital and image signatures — separate annotation objects with their own metadata.

Flattening removes the layer distinction. After flattening, the field values, highlights, and signature images become permanent page content — visually identical, structurally unmovable. Once flattened, you can't open the field and change the value; you can't drag a highlight to a different spot; you can't delete an inline signature.

• After signing. A signed PDF where the signature is a separate annotation can be moved or deleted by the recipient. Flatten to lock it.
• Before sending a completed form. The recipient could open your filled-in W-9 and change the SSN otherwise.
• To guarantee cross-viewer consistency. Some viewers render form fields differently (or not at all); some strip annotations on save. Flattened content is just page content — every viewer renders it the same way.
• Before merging. Form fields from multiple source PDFs can collide on the same field names. Flatten each input first.
• Before web publishing. Flattened PDFs are smaller and render faster on the web.
• For archival. Long-term storage where you want guaranteed visual permanence.

1. Open Flatten PDF.
2. Drop your PDF onto the page.
3. Click Flatten. The locked-down version downloads instantly.

Flattening is one-way: there's no "un-flatten." Keep the original file if you might want to edit it again later.

• "Flattening is the same as making a PDF read-only." Not quite. Read-only via permissions can be removed with the password. Flattening physically removes the editability — it's structural, not policy.
• "Flattening encrypts the file." No. For encryption + password protection, use Protect PDF when it ships.
• "Flattening compresses the file." Sometimes slightly, but it's not a compression tool. Use Compress PDF for that.
• "My signature will become invalid after flattening." An image signature stays valid as page content. A cryptographic digital signature (PKCS#7) becomes invalid once you flatten — the cryptographic seal depends on the layer structure. If you need a verifiable digital signature, don't flatten after signing.

SwissArmyPDF's flatten operation handles:

• AcroForm fields (text, checkbox, radio, dropdown, signature). Values become static text/graphics.
• Annotations — highlights, underlines, strikethroughs, sticky notes (text content baked in), freehand pen strokes, shape annotations.
• Image-based signatures placed via signature pad.

It does not handle:

• Embedded files (attachments) — these are preserved as-is.
• Document metadata (title, author) — unchanged.
• JavaScript actions — removed entirely (this is intentional; they require an active form).

• Some annotations disappeared. A few annotation types (notably 3D and rich-media) aren't representable as flat page content. Their appearance is dropped during flattening.
• The file got bigger, not smaller. Flattening converts vector annotations to embedded graphics, which can grow file size. Run Compress PDF after if size matters.
• I need to edit it again. Open the original (pre-flatten) file. Flattening is one-way.
• The recipient says fields are still editable. They may be opening the original. Confirm you sent the flattened version.

Flattening usually happens to signed contracts, completed forms with personal information (SSNs, addresses, IDs), and final-state documents you're about to deliver. Uploading these to a web service means your most-sensitive PDF state briefly lives on someone else's server. SwissArmyPDF runs flattening entirely in your browser using pdf-lib. The pre-flattened file never leaves your device.

• Compress PDF — shrink the flattened file for delivery.
• Merge PDF — combine flattened sections into a final bundle.
• Sign PDF — add a final signature before flattening.
• Watermark PDF — mark the flattened copy as final or original.