Watermark PDF

Unlike HTML and CSS, which use explicit z-index properties to determine what renders on top of what, a PDF engine renders objects purely based on the chronological order they appear in the page's Content Stream.

The first object in the stream is drawn on the very bottom layer. The last object in the stream is drawn on the very top layer, overlapping everything underneath it.

When you add a watermark, this tool injects new rendering instructions (like Tj for text and rg for color) into the PDF's content stream.

• Foreground Watermarks: We append the instructions to the very end of the stream. This guarantees the watermark renders over everything else.
• Background Watermarks: We prepend the instructions to the very beginning of the stream. The watermark is drawn first, and the original document text is drawn over it.

Many users think a watermark provides cryptographic security. It does not.

Because a PDF is a collection of distinct vector objects, a watermark is simply an additional text object floating above your document. Anyone with a dedicated PDF editor (like Adobe Acrobat Pro) can simply click the watermark text and press delete.

To truly prevent unauthorized modification, you must apply an owner password that explicitly disables the "Modify Contents" permission flag (which you can do with our Lock PDF tool).