Stamping Watermarks onto Your PDFs
What this tool does
This tool lays a watermark over every page of a PDF. In text mode you type the word or phrase you want stamped -- CONFIDENTIAL, DRAFT, a copyright line -- then choose its color and font size. In image mode you upload a PNG or JPG logo and scale it to fit. Whichever you pick, you then control three things: opacity, rotation, and where the mark sits on the page.
The stamped file is rebuilt with pdf-lib, and a preview of page 1 shows how the result will look before you download it.
When to use it
Watermarks are how you signal the status or ownership of a document. A CONFIDENTIAL or DRAFT stamp warns readers that a file is internal or unfinished; a semi-transparent logo brands an exported report or proposal; a copyright line on a portfolio or price list discourages people from passing it off as their own. Because the mark is baked into the page rather than sitting on a separate layer, it travels with the document wherever it is opened or printed.
Example: a diagonal CONFIDENTIAL stamp
Say you want the classic diagonal warning. Switch to text mode, type CONFIDENTIAL, and give it a red color. Set the rotation to around 45 degrees and drop the opacity to roughly 25 percent so the underlying text stays readable. Choose the tile position to repeat the phrase across the full page instead of showing it once. Apply, and every page of the PDF carries the same diagonal stamp, ready to download.
Notes and edge cases
The opacity slider runs from 5 to 100 percent, so you can go from a faint background mark to a solid overlay. Rotation combined with the tile position gives the repeating diagonal look, while single positions like center or a corner suit a discreet logo. Every page is stamped in one pass. If your watermark text uses Korean, Japanese, or Chinese characters, a Noto Sans CJK font is loaded automatically, since the standard PDF fonts cover only Latin glyphs -- any character with no matching glyph is flagged so you can adjust it. Password-protected PDFs must be unlocked first, and PNG logos with transparency give the cleanest result because the see-through areas let the document below show.