PDF Watermark Remover

Remove image-based watermarks from PDF files by surgically deleting the drawing instructions from content streams and removing XObject resource references. This produces clean results with no visible artifacts (no white/black rectangles, no color mismatches).

When to Use

• User wants to remove a watermark from a PDF

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• User says "去水印", "remove watermark", "去掉水印", "去PDF水印"
• PDF has a "Made with Gamma", Canva, or similar branded watermark
• PDF has an image-based watermark in a corner or specific position

How It Works

The removal process targets the root cause — the PDF content stream instructions that draw the watermark image — rather than covering or replacing the image:

1. Detect: Scan each page for images matching watermark characteristics (position + size)
2. Map: Build XObject name-to-xref mapping from the page's resource dictionary
3. Remove from content stream: Delete the q...cm.../Name Do...Q drawing instruction
4. Remove from resources: Delete the watermark entry from the XObject dictionary
5. Save with garbage collection to clean up orphaned objects

This approach leaves zero visual artifacts because the watermark simply never gets drawn.

Workflow

Step 1: Analyze the Watermark

Before running the script, determine the watermark's characteristics:

1. Open the PDF and identify the watermark visually
2. Note its position (typically bottom-right corner) and approximate size
3. If it's a link (clickable), note the domain (e.g. gamma.app)

Step 2: Run the Removal Script

Execute scripts/remove_watermark.py:

python scripts/remove_watermark.py <input.pdf> <output.pdf> [options]

Common options:

Gamma watermark example:

python scripts/remove_watermark.py input.pdf output.pdf --remove-links --link-domain gamma.app

Custom position watermark (e.g. top-left):

python scripts/remove_watermark.py input.pdf output.pdf --x-threshold 0 --min-w 50 --max-w 300 --min-h 10 --max-h 80

Step 3: Verify

Open the output PDF and check:

• Watermark is completely gone (no visual remnants)
• No color patches, rectangles, or artifacts in the watermark area
• Page content is otherwise intact

Troubleshooting

Key Technical Insight

Why not overlay/replace? Three approaches that DON'T work well:

1. White rectangle overlay — Visible on non-white backgrounds, misses rounded corners
2. Image data replacement with 1x1 pixel — PDF renders the 1x1 pixel scaled up as a colored rectangle (black for transparent, white for white pixel)
3. delete_image API — Only clears image data, doesn't remove the XObject reference or content stream Do instruction; renders as blank/colored rectangle

The correct approach (used by this skill): Delete the Do instruction from the content stream and the /Name xref R entry from the XObject dictionary. The watermark image data becomes an orphaned object that gets garbage-collected on save.

Requirements

• Python 3.8+
• pymupdf (pip install pymupdf)

这是一个功能可靠的 PDF 水印移除工具，能有效清除图片水印且不留痕迹。文档说明详细清晰，命令行参数设计合理。主要局限是只能处理图片水印，对文字类水印无能为力；使用时需要手动调整参数判断水印位置和大小，对新手不太友好。整体适合有技术基础的用户使用。