PDF Document Synchronous Scrolling Tool - Compare Two PDFs Side-by-Side

it365 Toolbox

File 1 (Left)

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File 2 (Right)

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Select or drag PDF file here

Scroll Sync Mode

Offset Alignment Mode

Allows keeping the current scrolling offset. When one document is scrolled, the other automatically moves by the exact same distance. This is highly flexible for comparing two documents that have uneven chapter distributions, paragraph displacements, or different total page counts.

Absolute Alignment Mode

Forces double window relative percentage locking. Scrolling on one side instantly aligns the other to the exact identical relative percentage height. Ideal for reviewing identical layout drafts, contract updates, and word-by-word audits.

Steps & Tips to Compare Two PDF Files Online

Welcome to the Free Online PDF Document Synchronous Scrolling Tool. Designed to help you compare differences between two PDF files efficiently, this tool allows you to open two PDF documents side-by-side on a single screen and scroll them in perfect sync. This is extremely helpful for verifying contract versions, auditing translations, comparing source drafts, or reviewing layout updates.

No document data is uploaded to any remote server. The entire parsing and rendering processes run securely in your local browser memory, protecting your business confidentiality. Works across Windows, Mac, iOS, and Android.

Quick 3-Step Start

🎈 Step 1: Upload PDF Documents to Compare

Click the upload areas on the left and right panels or drag your local PDF files directly into the respective comparison panes. The tool will parse and render your documents locally using high-fidelity rendering engines.

🎈 Step 2: Scroll to Inspect Differences

Scroll in either pane. The other pane will follow automatically. You can toggle sync scrolling on/off, change zoom factors, or adjust sync alignment modes inside settings.

🎈 Step 3: Clear and Load Next Files

Simply click "Clear" at the top of either document column to release memory and make room for your next comparison batch.

Offset vs. Absolute Scroll Sync Modes

To handle complex paragraph offsets and different layouts, we developed two smart scroll synchronization modes. Click "Settings" to switch anytime:

• Offset Alignment Mode (Recommended): Preserves any pre-existing scroll offset. If the same paragraph is on page 2 in File 1 but page 3 in File 2, you can align them manually first, then start scrolling. The system calculates the scroll delta and keeps the offset constant.

• Absolute Alignment Mode: Keeps both views locked at the exact same relative vertical scroll percentage. Best for comparing documents that share identical layouts and formatting page-for-page.

Swap Viewports Instantly

During dual-file auditing, you may want to swap the left and right positions to match your reading patterns. We provide a pure CSS "Swap Positions" feature:

Click "Swap Positions" to visually reverse the two document viewports using CSS Flexbox configurations. Note that the top headers ("File 1" and "File 2") and their file metadata cards stay in place. Only the document contents swap visual columns, helping you track which file belongs to which slot while offering ergonomic flexibility.

Why Use Our PDF Synchronous Comparison Tool?

• 100% Privacy Protection: Runs completely offline in your browser. Files never touch our servers, guaranteeing the confidentiality of your financial drafts, agreements, or transcripts.

• Full-Width and Responsive Layouts: Adapts to PC browsers by extending to full window width for maximum side-by-side reading space. Automatically shifts to an optimized top-to-bottom layout on mobile devices.

• Text Selection and High-Definition Copying: Renders documents in HD. The text layers are layered on top of the canvases, allowing you to select and copy text strings directly for quick copy-pasting.

Side-by-Side Comparison

Open two PDF documents side-by-side on a single screen to spot changes and layout disparities instantly, boosting audit efficiency.

Offset Scroll Sync

Preserve layout offsets during scroll. Scroll delta matches perfectly between panels, perfect for asymmetric file comparison.

Absolute Alignment Mode

Force both document views to align identically to the same vertical scroll percentage for precise layout auditing.

Swap Viewports instantly

Toggle CSS layouts to swap the document contents visually while keeping original slot headers and clear actions in place.

Millisecond Loading Speed

All processes happen locally inside browser sandbox. Offers near-instant rendering speeds with zero uploads required.

Full-Width Responsive

Expands to full width on PC screens for maximum reading space, and shifts to top-and-bottom columns automatically on mobile.

Strict Document Privacy

Your documents never touch our servers. Processing occurs entirely in your browser sandbox, keeping confidential files secure.

Copy Text and Headers

Text layer overlay aligns exactly to canvas. Allows selecting, copying, and pasting paragraphs directly to speed up auditing.

Zoom Memory Configurations

Adjust zoom values or sync modes freely. Options are stored automatically inside your localStorage and recovered on your next visit.