Overlay PDF With Letterhead or Stamp — Free Online Tool

How to Overlay Two PDFs Online

A PDF overlay merges two documents in the depth dimension instead of end-to-end. Rather than adding page B after page A the way a normal merge does, an overlay places one PDF directly on top of or behind another on the same page. That single difference is what lets you drop a company letterhead behind an existing invoice, stamp "DRAFT" across every page of a contract, or print a batch of certificates from one reusable template — all without redesigning the original file.

Step-by-Step

1. Upload your content PDF — This is the main document you want to keep. Its page size and orientation are preserved as the master.
2. Upload your overlay PDF — The template, stamp, watermark, or background you want to apply. If it has multiple pages, the first page is used as the stamp.
3. Choose Overlay or Underlay — Overlay sits on top (best for stamps and watermarks); Underlay sits behind (best for letterheads and backgrounds so your text stays readable).
4. Pick the pages — Apply to every page, or type a range like 1-3,5,7 to stamp only certain pages.
5. Combine and download — Preview the merged result, then download. The output keeps selectable text from the base document.

Overlay vs. Underlay: Which Should You Use?

The mode you pick decides what stays visible when the two layers cover the same spot:

• Use Overlay for semi-transparent stamps ("PAID", "CONFIDENTIAL", "APPROVED"), signature blocks, or watermarks that are meant to sit visibly over the content.
• Use Underlay for letterheads, branded borders, watermarked paper, or background graphics. Because the layer sits behind your text, nothing important gets hidden.
• Tip: If your stamp is fully opaque and you choose Overlay, it will hide whatever is beneath it. Use a transparent PNG-based overlay PDF, or switch to Underlay, to keep the base text legible.

Real-World Use Cases

• Letterheads at scale — Keep your documents plain in Word, then underlay your branded letterhead PDF at the end so every page matches your identity.
• Approval stamps — Overlay a "CONFIDENTIAL" or "APPROVED" mark across an entire policy document before circulating it.
• Certificates and diplomas — Combine one designed template with a content PDF of names so each output looks professionally printed.
• Invoices and quotes — Layer a footer with payment terms or a logo behind exported accounting PDFs.
• Event tickets and forms — Apply a fixed background design to variable ticket content.

What Happens When Page Sizes Differ?

The overlay PDF is automatically scaled to fit the content page's dimensions, and the content page size is always preserved as the master. So if you stamp an A4 letterhead onto a US Letter document, the letterhead is resized to match Letter rather than forcing your document to A4. For best alignment, design your overlay at the same page size as the document you'll apply it to.

Privacy

Both PDFs are processed entirely in your browser using pdf-lib. Neither your content document nor your template is ever uploaded to a server — which matters when the base file is a contract or an invoice. You can confirm this by going offline after the page loads; the overlay still works.

Frequently Asked Questions

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