Overlaying one PDF over another means placing the pages of a second PDF on top of the pages of a first PDF, producing a single new file where the second PDF's artwork sits above the first PDF's artwork on every page. The browser-based PDF Overlay tool does exactly this: you choose a base PDF and an overlay PDF, set an opacity between 0.1 and 1, and download a new PDF whose page count, page order, and page boxes come from the base document while the overlay artwork is drawn on top. Both files are read, embedded, drawn, and saved locally, and the original two files are never overwritten. The new file uses the base filename with "-overlay" added before the .pdf extension, so you can keep both inputs as your working copies. This is a visual layering operation, not a structural merge: the overlay becomes PDF artwork above the base page, centered and proportionally scaled to fit inside the base page rectangle, and the result is the kind of layered document you'd use to add a letterhead, a reusable border, or a transparent design layer on top of an existing report.
What it means to overlay one PDF over another
An overlay is a visual layering of two PDF documents on a single page canvas. The first PDF — called the base — defines the structure: how many pages the output will have, in what order, and what size each page is. The second PDF — called the overlay — contributes the foreground artwork that gets drawn on top. Both stay readable as separate documents while the new combined file shows them stacked.
Think of the base as the paper and the overlay as the printed layer placed on top. If the overlay is fully opaque, the base artwork may be hidden behind it; if it is partially transparent, both layers remain visible. The tool does not blend the two PDFs into a new structural document — the base PDF is still recognizably itself in the output, just with an extra drawing pass on top.
How PDF Overlay differs from merging and concatenating
Several PDF operations sound similar but do different things. Knowing which one you actually need saves time and avoids surprise results.
- Merge PDF concatenates two or more documents end-to-end. Page 10 of the second PDF becomes page 11 of the result, and the two documents never share a single page.
- Alternate Mix PDF interleaves pages from two documents in A1, B1, A2, B2 order and appends any leftovers. Each output page still comes from one source PDF, not both.
- Add Watermark to PDF stamps a generated text mark onto existing pages using a text label, font, size, color, and rotation you choose.
- PDF Overlay embeds an existing PDF on top of another existing PDF. The overlay is real PDF artwork, not generated text, so it can include shapes, signatures, design elements, or images that already live in another file.
Use PDF Overlay when you have a prepared visual layer — letterhead, border, stamp sheet, design template — and you want to place it on top of a content PDF without re-creating either document.
How to overlay one PDF over another in your browser
Follow these steps to layer one PDF on top of another using PDF Overlay. Each step is a deliberate choice that affects the final result.
- Open the PDF Overlay tool. Navigate to the tool in your browser. Everything from here on happens locally — no upload step, no account, no email.
- Pick your base PDF. This is the document whose page count and order you want to preserve in the output. Every output page comes from this file, and any page in the base that does not have a matching overlay page will simply appear unchanged.
- Pick your overlay PDF. This is the document whose pages will be drawn on top of the base. Both files must be non-empty PDFs no larger than 25 MiB. Encrypted, damaged, or unsupported files will produce a visible error rather than a partial result.
- Set the opacity. Move the opacity slider from 0.1 (most transparent) to 1 (fully opaque). Lower values let more of the base page show through; 1 paints the overlay at full strength. Existing transparency inside the overlay page is preserved as part of that artwork.
- Review the page-mapping rule. A single-page overlay repeats on every base page. A multi-page overlay maps page 1 to base page 1, page 2 to base page 2, and so on. Pick the overlay that matches the workflow you want.
- Create the overlaid file. Click the action button. The tool embeds the overlay pages into the base document, fits each overlay page proportionally inside the corresponding base page, centers it, and serializes a new PDF.
- Download the result. The download uses the base filename with "-overlay" added before the .pdf extension, so a base called quarterly-report.pdf becomes quarterly-report-overlay.pdf. Your original two files stay untouched.
- Open every important page and inspect the result. Check the corners, the center, and the edges where the overlay meets the base. Verify that nothing important from the base is hidden and that the overlay sits where you expect.
How page mapping and opacity actually work
PDF Overlay follows two explicit mapping rules, and understanding them up front prevents wasted iterations.
| Scenario | Overlay page count | Mapping behavior | Effect on base |
|---|---|---|---|
| Reusable foreground layer (letterhead, border, stamp sheet) | 1 | The single overlay page is repeated on every base page. | Every base page receives the same overlay. |
| Page-by-page foreground layer (matching sheets, signatures, design elements) | 2 or more | Overlay page 1 → base page 1, page 2 → base page 2, and so on. | Base pages beyond the overlay count remain unchanged; overlay pages beyond the base count are ignored. |
Opacity is independent of mapping. A value of 1 paints the overlay at full opacity, which can completely hide the base artwork beneath it on parts of the page. Smaller accepted values (down to 0.1) make the layer more transparent where the underlying PDF graphics model supports it, letting the base content show through. If your overlay PDF already contains transparent areas — a logo on a transparent background, for example — that built-in transparency is preserved and combined with the opacity you set.
How the overlay is positioned on each base page
Each applied overlay page is scaled uniformly to fit inside the base page. The aspect ratio is preserved, the fitted result is centered horizontally and vertically, and there is no cropping or stretching. The base page rectangle sets the boundary; the overlay simply fits itself inside that boundary as well as it can.
When the two page shapes differ, blank space can remain on two sides. A landscape overlay on a portrait base page, for example, will be sized to fit the narrower dimension and centered, leaving equal margins on the top and bottom. The tool does not offer fill-and-crop behavior, arbitrary offsets, rotation controls, alignment corners, or separate scaling for width and height — if you need any of those, prepare the overlay artwork at the exact target page size before using the tool.
What the overlay operation preserves and what it changes
Knowing what stays the same and what does not is the difference between a useful layered document and a confusing file.
Preserved from the base PDF: the page count, the page order, the page boxes, and the underlying content. The overlay is drawn afterward, so it appears above the existing base-page artwork where it is opaque.
Preserved from the overlay PDF: the artwork itself, including any vector content and text that the embedded library supports as vector. The overlay is embedded as PDF artwork, not as a screenshot, so text and shapes can stay sharp when the result is zoomed or printed.
Not preserved as interactive objects: links, comments, form fields, scripts, attachments, and outline destinations. The output is a visual page overlay, not a semantic merge of every document structure. If the base PDF contained fillable form fields or clickable links, they may still exist in the base content stream, but they are not guaranteed to remain functional after the overlay drawing pass.
Not changed: your original files. The base and overlay PDFs are never overwritten. The output is a brand-new PDF, named after the base with "-overlay" appended.
Not supported: encrypted, damaged, oversized (over 25 MiB), and incorrectly labeled files. Password protection is not bypassed; such files produce a visible error rather than a partial result.
Inspect the result before sharing or printing
A full-page opaque overlay can hide the base visually, and a dark overlay can reduce readability of the base even at partial opacity. Hiding content visually does not delete it from the base content stream, and it is not a secure redaction method. Similarly, placing a signature-looking image does not create a cryptographic digital signature or establish signer identity — for a real signature workflow, use a tool designed for that purpose.
Open the downloaded file and check at minimum: the first page, the last page, any page where the overlay meets a page boundary in the base document, and any page where the page sizes or orientations change. If the overlay is intended for print, run a professional preflight because the tool does not inspect blend modes, knockouts, overprint settings, spot colors, or printing separations.
Stale results are also handled automatically: changing either input file or the opacity revokes the previous download object URL and removes the obsolete result, so you are never working from an out-of-date overlay by accident.