Putting one PDF on top of another
Some documents are two things at once: a letterhead and a letter, a certificate template and a name, a form background and the answers, a branded frame and a report. Producing them usually means the design lives in one file and the content in another, and something has to combine them. This stamps every page of one PDF onto the pages of another.
Both files keep their vector content. Nothing is converted to an image, so the text of the base document stays selectable and searchable, the artwork stays sharp at any zoom, and the result is a fraction of the size a rasterised version would be.
What it is for
- Letterhead. Print a letter as a plain PDF, then lay the headed-paper design behind it. Cheaper than pre-printed paper and it survives being emailed.
- Certificates and templates. One designed background, many name pages.
- Branding a report exported from a system that offers no styling of its own.
- A stamp or seal on every page, when it exists as a one-page PDF rather than an image.
- Comparing two versions visually by laying one over the other at partial opacity — differences show as doubled text.
How the pages line up
| Overlay file | What happens |
|---|---|
| One page | Repeated on every page of the base document |
| Same number of pages as the base | Matched page for page |
| Fewer pages than the base | Matched in order, then the last overlay page repeats |
| More pages than the base | The extra pages are ignored — the base decides the page count |
Page size is not assumed to match. Stretching fills each base page exactly, which is right when both files are the same paper size and wrong when they are not — an A4 overlay stretched onto Letter will distort slightly. The two proportional options scale the overlay to fit without distorting it.
Opacity, and what sits on top
The overlay is drawn over the base content, so at full opacity it covers whatever is underneath. For a letterhead that is usually fine — the design lives in the margins, and the letter text sits in the middle where the design is empty. For a background template it is not, and lowering the opacity to somewhere between 10 and 30 per cent keeps the base readable.
If the design must genuinely sit behind the text rather than in front of it, the reliable route is to reverse the roles: make the template the base file and the content the overlay. The one on top wins, and choosing which file is which is the whole control you need.
Things worth knowing
- Form fields, links and bookmarks from the overlay are not carried across — only its drawn content is stamped.
- The base document keeps its own text, links and structure; it is edited, not rebuilt.
- Encrypted files must be decrypted first. An encrypted PDF cannot be read at all until the password is removed with Unlock PDF.
- For plain text across a page, PDF Watermark is simpler — it needs no second file and handles rotation and tiling.
- Check one page before sending. Opacity and placement are easy to get slightly wrong and obvious once you look.