How do I overlay one PDF on another?

Open PDF Overlay, upload the base PDF, upload the overlay PDF, choose opacity, layer, position, and page alignment, then process and download the combined file.

What is PDF overlay used for?

PDF overlay is used for adding letterhead, stamps, signature blocks, seals, form backgrounds, page templates, and full-page watermarks to an existing PDF.

Is overlaying the same as merging PDFs?

No. Merging places pages one after another. Overlaying stacks one PDF page on top of another so both appear on the same page.

Can I overlay a letterhead behind my document?

Yes. Use the Behind content layer for letterhead or stationery so the document text stays readable above the design.

Can I overlay only the first page?

Yes. Use Single Overlay on First Page Only when you need a stamp, seal, or signature page only at the beginning of the document.

PDF How-To Guides

How to Overlay One PDF on Another Online for Free

By The OptaPDF Team • Published August 26, 2026 • 7 min read

If you need to put a letterhead, stamp, signature page, watermark, seal, or form background onto an existing PDF, you do not want Merge PDF. You want PDF Overlay. Overlaying stacks one PDF on top of another on the same page, so both layers appear together in the downloaded file.

How to overlay one PDF on another

Open PDF Overlay.
Upload the base PDF. This is the document you want to keep.
Upload the overlay PDF. This can be a letterhead, stamp, signature, watermark, or template.
Choose the overlay layer: Over content for stamps and signatures, or Behind content for letterhead.
Adjust opacity, position, and page alignment while watching the live preview.
Process and download the final layered PDF.

Overlay vs merge: the important difference

Merge PDF joins pages end-to-end. If you merge a two-page document with a one-page letterhead, you get three pages. Overlay PDF places the letterhead on the existing pages, so the finished document keeps the same page count while adding the design or stamp to each page.

Best settings for common overlay jobs

Job	Best layer	Recommended setting
Company letterhead	Behind content	Overlay first page on all pages
APPROVED or PAID stamp	Over content	70-100% opacity, center or corner
Faint watermark	Over content	20-40% opacity
Signature block	Over content	Single overlay on first page only
Form background	Behind content	Match pages one-to-one

How page alignment works

If both PDFs have the same number of pages, use Match Pages. Page 1 overlays page 1, page 2 overlays page 2, and so on. If your overlay is a single-page letterhead, use Overlay First Page on All. If only the cover page needs a stamp or signature, use Single Overlay on First Page Only.

How to avoid covering important text

For letterheads and stationery, use the behind-content layer and keep the opacity readable. For stamps or signatures that need to be visible, use over-content mode but place the overlay away from the main text. The live preview is the important part: check the first page and a later page before exporting.

Is PDF overlay private?

OptaPDF PDF Overlay runs in your browser with pdf.js and pdf-lib. That means the base PDF and overlay PDF are processed on your device instead of being uploaded to the server. For sensitive documents, that is a meaningful privacy advantage. For heavier jobs such as OCR, Office conversion, and deep compression, use the matching server-side tool and rely on OptaPDF's 30-minute deletion policy.

Related tools

Use Watermark PDF for repeated text or logo marks, Sign PDF for electronic signatures, Edit PDF for manual annotations, or Merge PDF when you need pages one after another instead of layered on top of each other.