You have a generated PDF — an invoice from your accounting software, a report exported by an internal tool, a contract template — that needs your company letterhead on every page before it goes out. The letterhead already exists as a designed PDF (built in Word, InDesign, Illustrator, Canva). You don't want to re-build the letterhead as plain text inside a generic watermark tool, and you don't want to manually paste it page-by-page in Acrobat. This guide covers the "overlay" technique for stamping one PDF onto another, how it differs from watermarking and merging, and how to get clean output.
The three different things "stamp a PDF" can mean
The terminology in PDF tools is confusing. Three operations sound similar but produce very different results:
1. Merge
Merges PDFs sequentially — one after another, in pages. If PDF A has 3 pages and PDF B has 2 pages, the merged output has 5 pages: A1, A2, A3, B1, B2. Use Merge when you want to append one document to another.
2. Watermark
Generates a text stamp with a font, size, opacity, and angle (e.g. a grey "CONFIDENTIAL" rotated 45° across each page). Use Watermark when the stamp is just text and you want fine control over the typography from a simple form.
3. Overlay (this guide)
Places one PDF on top of another — like sliding a transparency sheet over each page. If your letterhead is already designed as a PDF (logo, header text, brand colours, footer block), Overlay reuses that PDF as-is. No re-typing into a generic stamp form, no losing the brand design.
If you have a letterhead PDF already, Overlay is the right tool. If you just need "DRAFT" text in red diagonally across each page, Watermark is faster and more flexible.
How PDFGrover's PDF Overlay works
Our PDF Overlay tool runs entirely in your browser. It uses a pure-JavaScript PDF manipulation library to load both PDFs, stamp the overlay onto every base page, and emit a new PDF on your device. Nothing is uploaded to our server. For workflows involving confidential contracts or internal financial reports, that matters.
The technique under the hood, in three steps:
- Copy the overlay PDF's page into the base PDF's document context. This translates the overlay's fonts, images, and vector content into the base document's resource pool.
- Embed the copied page as a reusable form-XObject. This makes the overlay a single drawable graphic that can be placed anywhere on a page like a stamp.
- Draw the embedded form on every base page at the origin. PDF coordinates have the origin at the bottom-left, so a full-page overlay matching the base's dimensions covers the entire page exactly.
The result is a brand-new PDF where every base page now carries the overlay's design on top, with the base content underneath visible wherever the overlay is transparent.
What gets preserved
- Base page content — text, images, fonts, hyperlinks: all stay exactly as they were. Selecting text on the base content still works.
- Page dimensions — output pages match the base PDF's sizes. If your base is US Letter and your overlay is A4, output stays US Letter; the overlay is anchored to the base's bottom-left corner and may not cover the full page.
- Fonts and vectors in the overlay — overlay text stays vector text (not raster), so it scales cleanly at any zoom and stays sharp on retina screens.
- Per-page overlay variation (if you want it) — see below.
The multi-page overlay trick
If your overlay PDF has multiple pages, PDFGrover applies them in order. Page 1 of the overlay lands on page 1 of the base, overlay page 2 on base page 2, and so on. When the base has more pages than the overlay, the last overlay page repeats for every remaining base page.
This means you can do useful things with a multi-page overlay:
- Different first-page letterhead, plain subsequent pages: build a 2-page overlay where page 1 has the full letterhead and page 2 is a blank PDF. Apply to a 10-page base, and only page 1 carries the letterhead — pages 2-10 stay clean. Useful for "first-page letterhead + plain continuation" formal documents.
- First page + watermark for the rest: page 1 of the overlay is the full design; page 2 is just the "DRAFT" stamp. Applied to a 5-page base, page 1 gets the full design, pages 2-5 get the DRAFT stamp.
- Front matter + body matter: page 1 is a cover, page 2 is the inner header, page 3 is the back-matter footer. Applied to a 30-page base, page 1 gets the cover overlay, page 2 gets the inner-header overlay, pages 3-30 all get the back-matter overlay (the last overlay page repeats).
For the typical "letterhead on every page" case, just use a single-page overlay — PDFGrover will apply it to every base page automatically.
Limitations to watch for
Opaque overlays cover content
If your overlay PDF has a solid white background (or any non-transparent fill that covers the page), the base content underneath disappears. Letterheads designed in Word usually have a transparent page background — the only filled regions are the visible header / footer graphics. But letterheads exported from some design apps default to a solid white page background that needs to be removed before export.
To check: open your overlay PDF in Acrobat or any viewer and look at the background. If you see white, you'll get white. Export the overlay from your source app with transparency baked in (Save as PDF → Options → "Preserve transparency" or similar, depending on the app).
Size mismatch produces misaligned overlays
The overlay is anchored to the base page's bottom-left corner (PDF origin). If your overlay is the same dimensions as your base, the alignment is perfect. If the overlay is smaller than the base, it appears in the bottom-left quadrant. If it's larger, it overflows past the top-right.
For pixel-precise alignment, the overlay should be exported at the same page dimensions as the base. Most letterheads are designed for US Letter or A4 — make sure your base is the same size.
Encrypted PDFs
PDFs locked with an open password need to be unlocked first via our Unlock PDF tool before they can be overlaid. The Overlay tool will prompt you for the password if the source is encrypted.
Walk-through: stamping a letterhead
- Open PDFGrover PDF Overlay.
- Upload your base document first (the contract / invoice / report). The first PDF you upload is the base.
- Upload your letterhead overlay second. This is the PDF that will be stamped on top.
- The preview shows two thumbnails side by side — the base on the left, the overlay on the right — so you can confirm you've put them in the right slots.
- Click Apply Overlay. The in-browser engine copies the overlay into the base's resource pool, embeds it, and draws it on every page. For a 10-page base this typically takes under a second.
- The combined PDF downloads automatically. Open it and confirm the letterhead landed on every page, and that the base content underneath is still readable wherever the overlay is transparent.
That's the whole flow. No upload, no signup, no watermark on the output (other than your own intentional letterhead).
When to use Overlay vs other tools
| What you have | Right tool |
|---|---|
| A designed letterhead / stamp / seal as a PDF | PDF Overlay (this tool) |
| Just text ("DRAFT", "CONFIDENTIAL") with style controls | Watermark PDF |
| Two complete documents you want to append | Merge PDF |
| A signature you want on specific pages, not every page | Sign PDF |
| A logo image (PNG/JPG) to add to every page | Convert the image to a PDF first (JPG to PDF), then Overlay |
The wrong choice will frustrate you: trying to recreate a designed letterhead inside a generic text-watermark form is painful; trying to merge a letterhead document with your content will produce 10 pages of content followed by 1 page of letterhead, not letterhead-on-content.
Privacy and file handling
Both PDFs are loaded entirely into your browser memory, processed client-side, and the combined PDF is generated and downloaded directly from your browser. Nothing is uploaded to our server. No signup. No watermark on the output. Close the tab and both source PDFs disappear from memory; there's nothing on our side because nothing was ever on our side.
This is exactly the privacy story you want for the typical Overlay workflow: company letterheads applied to confidential contracts, proposals, and internal reports.
Further reading
- Tool page: PDF Overlay — interface, supported page sizes, encryption handling
- For text-only stamps with style controls: Watermark PDF
- For appending rather than layering: Merge PDF
- For a single signature: Sign PDF
- For encrypted source PDFs: Unlock PDF first, then overlay
Add a letterhead to your PDF now — free, no upload, runs entirely in your browser.