The fastest way to spot differences between PDFs
The method you choose depends on what you're comparing and whether you need to mark up the differences. For simple visual checks — comparing two versions of a contract, a before-and-after design, or similar documents — opening both PDFs in separate windows and viewing them side by side works fine. For detailed line-by-line comparison or when you need a report of every change, dedicated comparison tools are faster and more reliable.
Most PDF readers built into Windows and macOS can open multiple windows. Paid PDF software like Adobe Acrobat Pro includes a built-in comparison feature that highlights changes automatically. Free online tools and standalone programs also exist, though they vary in speed and how much detail they show.
Key Takeaways
- Opening two PDFs in separate windows on your screen works for quick visual comparison but requires you to spot differences manually.
- Adobe Acrobat Pro's Compare Documents feature automatically highlights additions, deletions, and moved text in a side-by-side view.
- Free online comparison tools like Diffchecker and DiffPDF work without installing software, though they may have file size limits or require you to upload documents to their servers.
- Standalone desktop programs like Beyond Compare and WinMerge offer detailed comparison reports and work offline, which matters if your PDFs contain sensitive information.
Opening two PDFs side by side in your PDF reader
This is the simplest method and requires no additional software. Open your first PDF in your default PDF reader, then open the second PDF in a separate window. On Windows, use the Windows key + arrow keys to snap each window to half your screen. On macOS, open the first PDF, then hold Shift and click the green maximize button in the top-left corner to enter split-screen mode, then open the second PDF in the new pane.
This approach works well when you're checking whether two documents are identical or spotting obvious visual differences like missing sections, different images, or layout changes. You'll need to scroll through both documents manually and compare them yourself. It's slower for detailed changes like edited sentences or small number corrections, and you can't generate a report of what changed.
Using Adobe Acrobat Pro's Compare Documents feature
If you have Adobe Acrobat Pro (the paid version, not the free Reader), the Compare Documents tool automatically finds and highlights differences. Open Acrobat Pro, go to Tools in the top menu, select Compare Files, then choose your two PDFs. The tool shows a side-by-side view with additions highlighted in blue, deletions in red, and moved content in yellow.
The comparison generates a detailed report listing every change by page and type. You can filter the report to show only certain kinds of changes, zoom into specific sections, and export the results. This is the fastest method if you have the software, but Acrobat Pro costs money — Adobe offers a monthly subscription or a one-time purchase option.
Free online comparison tools
Several websites let you upload two PDFs and compare them without installing anything. Diffchecker (diffchecker.com) accepts PDFs and shows differences in a split view. DiffPDF (diffpdf.com) is designed specifically for PDFs and highlights changed text. Both are free to use, though they may limit file size or the number of comparisons per day.
The trade-off with online tools is that you're uploading your documents to someone else's server. If your PDFs contain confidential information, sensitive data, or proprietary content, this may not be acceptable. Read the privacy policy of any tool you use. Most delete files after a set time, but there's no may provide. Online tools are best for non-sensitive documents or when you need a quick comparison and don't want to install software.
Standalone desktop programs for detailed comparison
Programs like Beyond Compare, WinMerge, and Meld are designed to compare files of many types, including PDFs. Beyond Compare (Windows and macOS) shows a detailed side-by-side view with differences highlighted and lets you generate reports. WinMerge (Windows) and Meld (Linux and macOS) are free and open-source. These programs work offline, so your documents never leave your computer.
Desktop programs are slower to learn than built-in features but offer more control over how comparisons are displayed and reported. They're useful if you compare PDFs regularly or need to handle sensitive documents. Most have a learning curve steeper than online tools, but they're worth it if comparison is part of your regular workflow.
What each method shows you
| Method | What it highlights | Cost | Best for |
|---|---|---|---|
| Side-by-side windows | Visual differences only; you spot them | Free | Quick checks, obvious changes |
| Adobe Acrobat Pro | Text additions, deletions, moved content in color | Paid subscription or one-time purchase | Detailed text changes, professional reports |
| Online tools (Diffchecker, DiffPDF) | Text differences highlighted; varies by tool | Free | Non-sensitive documents, no installation needed |
| Desktop programs (Beyond Compare, WinMerge) | Detailed differences with filtering and reporting | Free or paid | Regular comparisons, sensitive documents, offline use |
Choosing the right method for your situation
Start with the simplest option that solves your problem. If you're comparing two versions of a flyer or poster and just need to see if they look the same, side-by-side windows take 30 seconds to set up. If you're tracking changes in a contract or legal document and need to know exactly what changed, Adobe Acrobat Pro or a desktop program is worth the time investment.
For one-off comparisons of non-sensitive documents, an online tool is fastest. For regular comparisons or documents you can't upload to the internet, install a desktop program once and use it repeatedly. If you already subscribe to Adobe Creative Cloud or Office 365, check whether your plan includes Acrobat Pro — many do, and you may already have access to the Compare Documents feature.
Frequently Asked Questions
Can I compare PDFs on my phone or tablet?
Most PDF readers on mobile devices don't support split-screen comparison. Your best option is to use an online comparison tool on your phone's web browser, though the small screen makes it harder to see details. For serious comparison work, a desktop or laptop is more practical.
What if the two PDFs have different page sizes or orientations?
Side-by-side viewing and most online tools will display them as-is, which can make comparison difficult. Adobe Acrobat Pro and desktop programs like Beyond Compare handle this better by scaling or aligning pages automatically. If you're comparing documents with different layouts, a dedicated tool is worth using.
Do online comparison tools keep copies of my documents?
Most delete files within hours or days, but policies vary. Check the privacy policy of the specific tool before uploading sensitive documents. If you're unsure, use a desktop program instead — your files stay on your computer and never leave it.
Can I compare more than two PDFs at once?
Most tools compare two documents at a time. If you need to compare three or more, you'll compare them in pairs — first document A against B, then B against C. Some desktop programs like Beyond Compare let you set up multiple comparison windows, but this is less common in online tools.
What if one PDF is scanned and the other is text-based?
Scanned PDFs are images, not searchable text. Most comparison tools will show them as images and can't detect text changes the way they would in a text-based PDF. Adobe Acrobat Pro can sometimes recognize text in scanned documents, but results vary. For reliable comparison of scanned documents, visual side-by-side viewing is often your only option.