PDF Overlay Tool

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Base Layout (File A)

Drag & drop Original PDF here

Overlay (File B)

Drag & drop Revised PDF here

Rendering Canvases...

Processing high-resolution vector data locally.

Best Free PDF Overlay Tool Online

Finding minute visual discrepancies between two versions of an engineering blueprint, architectural layout, or graphical design can be incredibly difficult with the naked eye. Our PDF Overlay Tool solves this by electronically stacking two documents and utilizing CSS rendering to highlight modifications, additions, and deletions instantly.

Why Use a Visual Diff Checker?

🔒 100% Client-Side Privacy

Architectural plans and corporate schematics are highly confidential. Our tool renders the vector data locally via HTML5 canvas in your browser. Files are never uploaded to a server.

⚡ Advanced Blend Modes

Go beyond simple opacity. By utilizing the "Difference" blend mode, identical vectors cancel each other out (turning black), allowing shifted lines and new text to glow visibly on the screen.

🎯 High-Resolution Rendering

We render your PDFs at high DPI scales internally, ensuring that even the thinnest CAD lines and smallest blueprint text remain crisp when overlaid.

How to Compare PDFs by Overlaying

  1. Upload the Base File: Drag and drop your original layout (V1) into the "File A" dropzone.
  2. Upload the Overlay File: Drag and drop your revised layout (V2) into the "File B" dropzone.
  3. Wait for Rendering: The tool will automatically parse the vector data and stack Page 1 of both documents onto the interactive viewer.
  4. Analyze Differences: By default, the tool uses the Difference blend mode. Any areas where the documents are identical will disappear into the background, highlighting only the changes. You can adjust the opacity sliders manually to "flicker" between versions.

Frequently Asked Questions (FAQ)

What is the difference between Multiply and Difference modes?

Difference Mode subtracts the pixel values of the top layer from the bottom layer. If the pixels are identical, the result is black (or invisible against a white background). This is the best mode for spotting shifted lines. Multiply Mode darkens the overlapping areas, making it great for seeing both layouts at once as if they were printed on transparent tracing paper.

Why did only the first page render?

To ensure maximum browser performance and prevent memory crashes (especially on mobile devices), this tool currently extracts and overlays only Page 1 of the uploaded documents. For multi-page blueprints, we recommend splitting the PDF beforehand.

Is my proprietary data safe?

Absolutely. The entire rendering process is handled by a local JavaScript engine (PDF.js) executing within your device's RAM. No data is transmitted over the internet.

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