How to stamp a PDF with text or a logo, build a PDF from photos, and turn PDF pages back into image files.
A watermark is a visible mark drawn onto the page. It signals intent: that a document is a draft, is confidential, or belongs to you. It is useful and it is honest.
It is not a security control. Anyone can open a watermarked PDF, and a determined person can remove or crop a watermark. If a document must not be read by someone, a watermark is the wrong tool; do not treat it as protection.
Text watermarks are drawn with the fonts built into the PDF format, which means no font file is embedded and the output stays small.
Those built-in fonts cover Latin characters only. If you enter text the fonts cannot draw — Chinese, Japanese, Korean, Arabic, Hebrew, or most emoji — the tool says so rather than failing halfway through writing the file. For those scripts, render your text as a PNG and use an image watermark instead.
An image watermark stamps a PNG or JPEG onto the pages — a company logo, a scanned signature, or a rendered non-Latin phrase.
A PNG with a transparent background gives the best result, because the transparent area lets the page show through instead of covering it with a white box. Width is set as a percentage of the page width, so the same setting behaves consistently across mixed page sizes.
This builds a PDF with one image per page, which is the usual way to send a set of photographed or scanned documents as a single attachment.
"Match each image" makes every page exactly the size of its image, which avoids white borders but produces a document with inconsistent page sizes. Choosing A4 or US Letter instead fits each image onto a uniform sheet, scaled to fit without cropping, which is what you want if the result will be printed.
The PDF format itself only carries PNG and JPEG images. Anything else you add — WebP, AVIF, GIF, BMP, or HEIC photos from an iPhone — is decoded by your browser and converted to PNG first. That conversion depends on your operating system: HEIC decodes on Apple devices, and on other platforms the tool tells you to convert the file first rather than failing silently.
Very large photos are reduced before being embedded. A 50-megapixel image would otherwise exhaust the memory a mobile browser allows a single tab, and the status line tells you when this has happened.
This renders each page to a PNG or JPEG. PNG keeps text edges sharp and is the better choice for documents; JPEG produces smaller files and suits pages that are mostly photographic.
Resolution is a trade-off against memory. Higher settings produce crisper images but allocate a much larger canvas per page, so the tool checks each page against a memory budget first and quietly renders a little smaller if a page would exceed it. When that happens it is stated in the result rather than hidden.
All pages are delivered as a single ZIP, named so they sort in page order.
Use images-to-PDF when you need one file to attach, print, or sign. Use PDF-to-images when you need to drop a page into a slide deck, a chat message, or a web page, or when something will only accept an image.
Converting a PDF to images and back is lossy: the text becomes a picture of text. It can no longer be searched, selected, or read aloud by a screen reader. Keep the original PDF whenever the text matters.