Open two PDF files, synchronize scrolling of two side-by-side document windows, and quickly compare document differences. Supports Windows, Mac, and mobile.
Allows keeping the current offset between documents. When one document scrolls, the other moves by the exact same distance. Great for comparing asymmetric or mismatched documents in different sections.
Locks the scroll positions proportionally. When you scroll to any point on one side, the other aligns to the exact same percentage. Best for comparing highly identical versions (e.g., contracts, drafts, or versions with identical layouts).
🎈 Step 1: Upload PDF documents to compare
Click "Select or drag PDF file here" on the left and right panels, or drag your local PDF files directly into the viewports. Once imported, the tool renders high-definition pages locally.
🎈 Step 2: Scroll to compare documents
When you scroll in either viewport, the other will automatically follow. Supports both Offset and Absolute alignment modes.
Welcome to the free online PDF scroll sync tool. This tool allows you to open two PDF files side by side and scroll them synchronously. It is extremely useful for contract version comparison, academic paper editing, and code/design document proofreading.
🛡️ Privacy & Security Guarantee: This tool does not upload your files to any server. All parsing and rendering are done locally in your browser to secure your confidential documents. Supports Windows, Mac, Android, and iPhone.
To accommodate complex layouts, we have developed two user-friendly alignment modes. Click the "Settings" button at the top to toggle between them:
• 🔗 Offset Alignment Mode (Recommended): Allows keeping the current offset between documents. Great for comparing asymmetric or mismatched documents in different sections. The tool records the difference (Delta) and auto-scrolls proportionally.
• 🎯 Absolute Alignment Mode: Automatically aligns the scrolling percentage of both documents. Best for comparing highly identical versions (e.g., contracts or drafts) to spot tiny revisions instantly.
During side-by-side document reviews, you might need to swap the left and right perspectives. We provide a pure CSS "Swap Position" action:
🔘 Clicking the "Swap Position" button will visually swap the left and right viewports using CSS Flexbox order styles. However, the headers ("File 1" & "File 2"), original filenames, and their clear buttons remain in place. This makes it easy to track the slots while exchanging the visuals.
• 🔒 100% Privacy Protection: Runs entirely on the client side. Your PDFs are read and rendered locally in browser memory, never uploaded to any servers, securing sensitive contracts or personal files.
• 📱 Responsive Layout: For desktops, the page spans full browser width to guarantee enough space. For mobile devices, it automatically adapts to a stacked vertical layout with sync scroll still supported.
• 📋 Text Selection & Copy: Renders clear Canvas pages overlaid with an invisible text layer. You can highlight and copy text directly from the PDF, boosting your workflow efficiency.
Compare documents side by side with seamless sync scroll, doubling translation and proofreading efficiency
When reading academic papers, textbooks, or foreign documents, open the source PDF and its translation side by side. Scrolling one side automatically moves the other for seamless comparison. Perfect for scholars, translators, and language learners.
Ideal for legal, sales, and audit professionals to check contracts, bids, or reports. Place draft vs final version, or original vs revised version side by side. Use Absolute Mode to lock the scroll bar and spot any differences, deletions, or edits immediately.
When evaluating technical solutions, you must cross-reference request for proposals (RFPs) with bidder proposal sheets. Offset Mode allows you to align mismatched sections or page numbers, ensuring every requirement is met.
After a major revision, authors must edit papers page by page according to reviewer comments. Open the original submission PDF on the left and the updated draft on the right. Scroll synchronously to check all modifications against the response letter.
When converting Word/Markdown to PDF or executing layout designs, bugs like displaced images, overlapping tables, or broken fonts can occur. Compare side by side to verify formatting and layouts match the original across hundreds of pages.
Open two PDF files side by side. Spot additions, deletions, or modifications easily and proofread much faster.
Designed for asymmetric documents. Keep any initial scroll offsets, and the other side will follow by the exact delta amount.
Locks vertical percentage scroll. Keeps both documents aligned at the same height, which is ideal for comparing identical drafts.
Swap panels visually using CSS Flex order instantly, while titles, filenames, and buttons stay at their original positions.
Read files locally. No file uploads needed, rendering large PDFs and turning pages with zero lag or latency.
Full-width horizontal layout on desktops. Mobile devices stack panels vertically while maintaining scroll synchronization.
All processes happen locally inside browser memory. Your sensitive files and contracts never touch any remote servers.
Not an image viewer. Renders text layers over canvas pages, allowing you to highlight and copy content easily.
Configure absolute or proportional zoom values. Settings, mode selections, and zoom offsets are auto-saved locally.