Question 1

Text watermark or image watermark — which should I pick?

Accepted Answer

Text is the fast path for one-off pages: CONFIDENTIAL, DRAFT v3, INTERNAL USE ONLY. Pick an image when you want a logo or a full-bleed banner — a transparent PNG reads best, JPEG works fine for photographic marks. The two are interchangeable; switch tabs and re-apply to compare outputs.

Question 2

What opacity will read without overpowering the page?

Accepted Answer

For dark grey text on a white page, 25–35% reads as light texture and remains legible against colored headings. 50%+ reads as an explicit stamp and starts to obscure fine print. For a light-colored image logo on a busy page, start at 60% and dial down if it bleeds body text. The slider goes to 5% for the barely-there watermark a quiet title page wants.

Question 3

What does "corner", "center", and "tiled" actually do?

Accepted Answer

Corner anchors the bounding box near one of the four page corners with a margin of 5% of the shorter page edge. Center centers the box. Tiled fills the page with a regular grid spaced 60% of the bbox dimension apart — the traditional bold CONFIDENTIAL pattern. Rotation rotates every stamp by the same angle.

Question 4

Will watermarking flatten or recompress my PDF?

Accepted Answer

No. PDF-lib stamps each page by adding new drawing operators to the existing content stream and leaves every page's source objects alone. Text in the original PDF remains selectable; the output file is byte-incremented, not re-rendered. Attachments, form fields, and outline/bookmarks survive intact when the source supports them.

Question 5

Can I watermark an encrypted or password-protected PDF?

Accepted Answer

No — open it locally first. The browser File API cannot read encrypted PDFs in-page. Remove the password in your normal viewer, drop the unlocked file here, then re-encrypt or password-share it wherever you store it. The original password is never sent anywhere, because the bytes never leave your tab.

Question 6

Is my PDF uploaded anywhere?

Accepted Answer

No. PDF5 ships its watermark engine inside the browser tab. Open DevTools, watch the Network panel — there is zero outbound file traffic while you stamp. The bytes stay in memory on your machine until your browser hands them back as a download.

Question 7

Does this work offline?

Accepted Answer

Yes, after the first page load. Both the PDF-lib write engine and the pdf.js render worker are cached by the browser, so airplane mode is fine — re-pick a PDF, re-tune the overlay, re-apply, and re-download without a connection.

Watermark a PDF. See it land before you stamp.

Choose your overlay, tune the placement, grab the stamped file.

Three steps. No upload stage.

Choose your overlay

Tune position, opacity, preview

Download the watermarked PDF

Questions that come up before the first stamp.

Open the tool. Watch your Network tab. Ship the watermarked file.