Compare PDF Online Free — Visual Diff & Text Diff Tool

Both PDFs are rendered at high resolution (up to 300 DPI) and compared pixel by pixel. Additionally, text is extracted for word-level comparison. You can view results in 5 modes: side-by-side with highlights, adjustable overlay, diff-only, text diff, or flicker toggle.

Text Diff extracts the actual text content from both PDFs and performs a word-level comparison. Deleted words appear in red with strikethrough, added words in green with underline. Navigate between changes with the prev/next buttons.

Flicker mode rapidly alternates between the original and revised page at a configurable speed (200ms-2s). This makes even subtle visual differences jump out, similar to blink comparison used by astronomers to spot changes.

Yes. Pages present in only one document are shown alongside a 'No page' placeholder, and the comparison correctly reports them as 100% different.

Yes. The sensitivity slider lets you control the pixel difference threshold from 'very sensitive' (catches slight color shifts) to 'major changes only' (ignores minor rendering differences). You can also choose the highlight color.

Yes. WhiskFile's Compare PDF tool is completely free with no signup required. All 5 comparison modes, export options, and settings are available without any account or payment.

Yes. The entire comparison runs in your browser using JavaScript. Your PDF files are never uploaded to any server — they stay on your device at all times. This makes it safe for confidential contracts, legal documents, and sensitive business files.

Overlay mode stacks the revised PDF on top of the original with an adjustable opacity slider (10%-100%). Slide to blend between documents and see exactly where content has shifted, moved, or changed. This is especially useful for design proofs and layout comparisons.

The text diff uses an LCS (Longest Common Subsequence) algorithm that matches words precisely. Deleted words appear in red with strikethrough, added words in green with underline. You can navigate between changes with prev/next buttons.

Yes, two export formats are available. Export as a visual comparison PDF showing original and revised pages side by side with diff highlights, or export a text diff report (.txt) listing all word-level insertions and deletions per page.

150 DPI is fastest and sufficient for most documents. 200 DPI is the standard balance of quality and speed. 300 DPI captures fine details like small fonts or technical drawings but takes longer to render.

Visual comparison (pixel diff, overlay, flicker) works on any PDF including scanned documents. Text diff requires selectable text — if your scanned PDF has an OCR text layer, text diff will work. For image-only scans, use WhiskFile's OCR PDF tool first.

Press 1-5 to switch between the five view modes. Use left/right arrow keys to navigate pages. Press + or - to zoom in and out. These shortcuts make it fast to review multi-page comparisons.

Yes. Compare PDF works on any device with a modern browser — iPhone, Android, iPad, tablets, Chromebooks, and desktop computers. No app download required. The interface adapts to your screen size automatically.

Compare PDF accepts PDF files as input and produces PDF output. The maximum file size is 50 MB on the free plan (500 MB for Pro users). There are no page count limits.