What this tool does
A watermark only works if it sits behind the document rather than on top of it, and that one requirement is the whole difficulty. Drawn the obvious way, a watermark lands over the text and makes the page unreadable, which is not a watermark at all. Getting it behind the content means rewriting how the page's drawing instructions are ordered, and this tool does that.
How it works
A page's content is a list of drawing instructions, executed in order, so whatever appears last is drawn on top. Adding a watermark the obvious way appends to that list, which puts it in front of everything. To place it behind, the instructions have to be inserted at the start of the list instead, and the page's object structure has to be normalised before and after so the insertion is legal. That is the difference between a watermark people can read through and one that makes a contract unusable.
Opacity is set through an extended graphics state rather than by choosing a pale colour, because a pale colour is simply a light grey that prints as light grey, while transparency is a real property of the drawing. This matters at print, where a watermark that looks right on screen can come out either invisible or heavy, so the value is exposed rather than chosen for you and the tool notes that the effect depends on the printer.
A single centred stamp can be cropped away, which defeats the purpose, so tiling repeats the watermark diagonally across the whole page. That is the arrangement used on draft contracts and confidential documents, and it is why removing the watermark means editing every page rather than covering one spot. An image watermark works the same way and takes the same z-order fix as the text version, which is the part that is easy to get wrong.
The honest limit belongs on this page rather than in small print. A watermark is a drawing instruction like any other, and anyone with a PDF editor can select it and delete it. It marks a document as belonging to somebody, and it discourages casual reuse, but it is not a protection mechanism and it does not survive anyone who is deliberately trying to remove it. Tools that advertise an unremovable watermark are describing something that does not exist.
Worked example
A contract draft has to go to a client clearly marked as a draft, without making the clauses unreadable.
- Enter DRAFT as the text and choose a tiled layout so it cannot be cropped out of one corner
- Set the opacity low enough to read the clauses through, and rotate it diagonally
- The watermark is placed behind the page content, so the text stays fully legible
- Apply to all pages, or list the pages that should carry it
A clearly marked draft whose clauses remain readable, sent without the file ever leaving your browser, and with the removal limitation stated rather than hidden.
Accuracy and limitations
- A watermark can be removed by anyone with a PDF editor, because it is a drawing instruction rather than a protection. It is a marking, not a lock.
- Transparent watermarks print differently depending on the printer, and a value that looks right on screen can come out too light or too heavy.
- Text watermarks use the standard fonts available to every reader, so no custom typeface can be chosen.
- An existing watermark is not detected or replaced. Applying a second one gives you two.
Frequently asked questions
- Can a PDF watermark be removed?
- Yes, by anyone with a PDF editor, because a watermark is a drawing instruction like any other piece of content and can be selected and deleted. It is a way of marking a document as a draft or as belonging to somebody, and it discourages casual reuse, but it is not protection and no tool can make it otherwise.
- Why does the watermark cover the text?
- Because content drawn last appears on top. A watermark added the obvious way lands in front of the document's own text. This tool inserts it at the start of the page's drawing instructions instead, so it sits behind the content and the text stays fully readable, which is the only arrangement that works as a watermark.
- Should I tile the watermark or centre it?
- Tile it if the point is to prevent casual reuse, because a single centred stamp can simply be cropped off and the page will then look unmarked. Centre it when the aim is a clean cover-page marking where the diagonal repetition would look untidy.
- Will a transparent watermark print properly?
- It depends on the printer, and this is worth testing on one page first. Transparency is a real property of the drawing rather than a pale colour, so the printed result can differ noticeably from the screen. A value that looks correct on screen can come out nearly invisible or unacceptably dark.
- Can I use my logo as the watermark?
- Yes, an image watermark is placed behind the page content using the same z-order fix as the text version, which is the part that is easy to get wrong. A transparent PNG works better than a JPG for this, since a JPG has no transparency and will show as a solid rectangle.
- Are my PDFs uploaded to add a watermark?
- No. The page instructions are rewritten in your browser and the file is handed straight back. A draft contract is exactly the sort of document you would not want to hand to a stranger's server, and this one never has to.