Modufile's Watermark PDF tool lets you add customizable text watermarks to every page of a PDF document. You can configure the watermark text, font size, color, opacity, and rotation angle — placing it diagonally, horizontally, or at any custom angle. The watermark is drawn as a native vector text overlay using pdf-lib, so the original PDF quality and searchability are fully preserved. Everything runs in your browser with no file uploads. This tool is commonly used to mark documents as "Draft," "Confidential," or "Sample," or to add branding to shared files.