PDF Overlay

PDF Overlay superimposes one document on another. The first PDF in the queue is the base, the second is the stamp, and every page of the stamp is embedded into the base as a reusable object before being drawn over the pages you name. The base is not rebuilt page by page: its text stays selectable, its images keep the data they arrived with, and the page count comes back exactly as it went in. The /Rotate entry on both files is composed as the stamp is placed, so a letterhead still lands the right way up on a page a scanner turned sideways.

How the stamp repeats is the setting that decides what the tool is for. Stamping page 1 of the overlay on every page is the default, and it is the letterhead case — one sheet applied throughout. Cycling walks the overlay in order and starts again from the top, so a two-page overlay alternates across the document. Pairwise matches page for page by position, overlay page 4 onto base page 4, and skips any base page numbered past the end of the overlay: a two-page stamp over a forty-page report marks two pages and leaves the other thirty-eight alone.

The whole job runs in this tab. pdf-lib reads both files on your own machine, composes them there and hands back the result, so neither document goes anywhere, and the tool keeps working with the network switched off once the library has loaded. Scale to fit resizes the stamp — enlarging a small one as readily as shrinking a large one — to the biggest size that sits inside the base sheet with its proportions intact; keeping the overlay's own size leaves it at its native dimensions. Either way it is centred, and the base pages field takes all, odd, even, a number, a range such as 2-5, or a list like 1,4-6,last.

Opacity runs from 5 to 100 per cent, and it is worth knowing exactly what it dims. The value is written as a fill-alpha graphics state wrapped around the placed page, so filled text, solid shapes and scanned images fade the way you would expect. Stroked artwork does not. Ruled lines, table borders, outlines and the vector strokes of a plan keep their full weight at every setting, because pdf-lib writes no matching stroke alpha when it places an embedded page. For a letterhead, a scan or a block of type the slider behaves; for line art exported as vectors it will not.

The rest of the limits are worth reading before a long run. Exactly two PDFs are accepted — a third in the queue is refused with a count rather than guessed at — and nothing in the file list swaps them once they are there, so a reversed pair has to be removed and queued again in the right order. Only what the overlay page draws comes through, because it is embedded as a content stream: hyperlinks, form fields and comment annotations sitting on that page are left behind, and an overlay that paints a solid background will hide the base text beneath it. There is no offset, corner or coordinate control, so anything that must sit in a margin has to be positioned inside the overlay file itself, and at its own size an oversized stamp is simply clipped by the edges of the base sheet.

Two rougher edges round it off. Every page of the overlay is embedded whether the chosen mode ever draws it or not, so a twenty-page overlay used only for its first sheet still carries all twenty into the saved file and the result is larger than the job needed. A page in the overlay with no content stream at all — a truly empty sheet, not one that merely looks blank — stops the run with pdf-lib's own wording rather than a message written for you, and it does so even when that page would never have been drawn. Encrypted files cannot be parsed, and re-saving invalidates a digital signature the base already carried.

Runs on your device. Your file is processed directly in this browser.