Compare two PDF documents side by side, overlay them, or generate a pixel-level difference map. All processing happens in your browser.
or click to browse your files
or click to browse your files
Comparing PDFs...
Visually compare two PDF documents in three simple steps. No software to install, no account to create.
Drag and drop or browse to select two PDF files — one in each upload zone. The first file is loaded as Document A and the second as Document B. Both files are read directly into your browser without being sent to any external server, ensuring complete privacy for sensitive documents.
Select one of three view modes: Side by Side to see both pages next to each other, Overlay to stack both pages with one rendered at 50% opacity so you can spot subtle shifts and alignment differences, or Difference to generate a pixel-level diff map that highlights every changed pixel in red and shows unchanged areas in grayscale.
Click Compare to render the results. Use the page navigation buttons to step through every page in both documents. The tool calculates and displays the difference percentage for each page, so you can quickly identify which pages have changed and how much they differ from each other.
A fast, private, and completely free way to compare PDF documents online without any limitations.
Compare as many PDF files as you need without any cost. There are no premium plans, no daily limits, no per-file charges, and no trial periods. Every feature of the PDF comparison tool is available to everyone, always.
Your documents never leave your device. All PDF comparison happens entirely in your web browser using JavaScript and PDF.js. We cannot see, access, or store your files at any point during the process. Your sensitive documents stay private.
Choose from Side by Side, Overlay, or Difference views. Side by Side shows both pages next to each other. Overlay stacks them with transparency. Difference generates a pixel-level map highlighting every change in red.
The difference mode compares every single pixel between both pages. Changed pixels are highlighted in red while unchanged areas are shown in grayscale. The tool also calculates an exact difference percentage for each page.
If your two PDFs have different page counts, the tool handles it gracefully. It navigates through the maximum page count and shows blank canvases for the shorter document's missing pages, so you can compare every page of both files.
Your comparison results are clean and accurate. We never add watermarks, branding, or any other markings to the rendered output. The comparison view shows exactly what is in your documents, nothing more.
Everything you need to know about comparing PDF documents, from common use cases to technical details.
Comparing PDF documents is essential in many professional workflows. Legal teams need to verify that contract revisions match the agreed changes and nothing was altered without authorization. Designers compare proof versions to ensure color accuracy, layout consistency, and that feedback was implemented correctly. Publishers review typeset proofs against previous versions to catch last-minute errors before printing. Quality assurance teams compare generated reports across software releases to detect regressions. Financial professionals verify that regulatory filings match internal records. In every case, having a reliable visual comparison tool saves hours of manual page-by-page review and catches differences that the human eye might miss.
ConvertKr's PDF comparison tool uses PDF.js to render each page of both documents as raster images in your browser. The tool then provides three ways to examine the results. In Side by Side mode, both rendered pages are displayed next to each other so you can visually scan for differences. In Overlay mode, both pages are drawn on the same canvas with the second document at 50% opacity, making alignment shifts, missing elements, and text changes immediately visible. In Difference mode, the tool performs a pixel-by-pixel comparison of both rendered pages. For each pixel position, it calculates the RGB difference between the two images. If the combined difference exceeds a threshold, that pixel is highlighted in red on a difference map. Unchanged pixels are converted to grayscale for context. This approach catches even the subtlest changes in text rendering, image placement, and page layout.
The Difference view generates a new image where each pixel is colored based on how much it differs between the two documents. Red pixels indicate areas where the content changed — this could be modified text, shifted images, altered colors, or added and removed elements. The brightness of the red corresponds roughly to the magnitude of the difference. Grayscale pixels show areas where the content is identical or nearly identical between the two versions. The tool also calculates an overall difference percentage for each page, which tells you what fraction of the page area has changed. A difference of 0% means the pages are pixel-identical, while higher percentages indicate more extensive changes. This quantitative measure helps you quickly triage which pages need detailed review.
Real-world document revisions often involve adding or removing pages. ConvertKr's comparison tool handles this gracefully by using the maximum page count between the two documents. If Document A has 10 pages and Document B has 12 pages, you can navigate through all 12 pages. For pages 11 and 12 where Document A has no corresponding page, the tool displays a blank canvas on Document A's side while showing Document B's content normally. In Difference mode, any page that exists in only one document will show as 100% different, since every pixel differs from the blank comparison. This approach ensures you never miss added or removed pages during your review.
Contract review is one of the most common use cases — comparing a draft contract with the signed version to ensure no unauthorized changes were made. Design proofing is another frequent application, where designers compare client-approved mockups with final production files. Academic researchers compare manuscript versions to track changes between revisions. Print professionals compare pre-press proofs with the final printed output scanned back to PDF. Software teams compare auto-generated reports across versions to catch formatting regressions. Government agencies compare regulatory submissions from different reporting periods. In every scenario, visual PDF comparison provides certainty that two documents either match or clearly shows exactly where they differ.
For the most accurate comparison, use PDFs that were generated at the same resolution and page size. If the documents have different page dimensions, the rendered images may not align perfectly, which could inflate the difference percentage. When comparing contracts or text-heavy documents, the Side by Side view is often the most practical starting point — you can visually scan both versions simultaneously. For design files where subtle color or layout shifts matter, the Overlay mode is invaluable. For automated or large-scale reviews where you need to quickly identify which pages changed, use the Difference mode and check the percentage — pages showing 0% are identical and can be skipped. If you need to compare specific pages rather than entire documents, consider using the Split PDF tool first to extract the relevant pages.
Common questions about comparing PDF files with ConvertKr.
The tool performs a visual, pixel-level comparison of rendered PDF pages. It can detect any difference that is visible when the pages are rendered — including text changes, font differences, color shifts, image modifications, layout changes, added or removed elements, and even subtle anti-aliasing differences. It compares what you would see on screen, not the underlying PDF structure.
Yes, but the results may be less meaningful if the page dimensions differ significantly. The tool renders each page at its native size, so pages with different dimensions will produce different canvas sizes. For the most accurate comparison, use PDFs with matching page sizes and orientations.
The difference percentage represents the fraction of pixels on the page that differ between the two documents. A value of 0% means the pages are pixel-identical. A small percentage like 2-5% might indicate minor text edits or moved elements. Higher percentages suggest more extensive changes. The threshold for counting a pixel as different is a combined RGB difference of 30 or more, which filters out insignificant rendering variations.
No. All processing happens entirely in your web browser using JavaScript and PDF.js. Your files never leave your device. ConvertKr cannot see, access, or store your documents at any point during the comparison process. This makes the tool safe for confidential, legal, financial, and personal documents.
Yes. Since the tool compares rendered page images rather than text content, it works equally well with scanned PDFs, digitally created PDFs, and mixed documents. Scanned pages are rendered as images and compared pixel by pixel, just like any other PDF content. However, slight scanning variations (different scan resolutions, alignment shifts, paper skew) may produce higher difference percentages even when the content is the same.
Yes. The PDF comparison tool is fully responsive and works on smartphones, tablets, laptops, and desktop computers. On smaller screens, the side-by-side view automatically stacks vertically for easier viewing. Any device with a modern web browser — including Chrome, Safari, Firefox, and Edge — can use the tool.
There is no hard limit on the number of pages in either PDF. Since processing happens locally in your browser, the practical limit depends on your device's available memory and processing power. The tool renders one page at a time, so even very long documents can be compared without loading all pages into memory simultaneously.
The tool is designed for comparing two documents at a time, which is the most common use case. If you need to compare three or more versions, compare them in pairs — for example, compare version 1 with version 2, then version 2 with version 3. This pairwise approach helps you track incremental changes across multiple revisions.
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