To compare two pages from separate PDF files on a Mac, open both in Preview, put each PDF in its own window, then tile the windows on the left and right sides of the screen. Choose the same zoom level and navigate each file to the page you want to inspect. Preview’s View > Two Pages command shows facing pages from one PDF; it does not compare a page from one PDF with a page from another.

Open the PDFs in separate Preview windows

In Preview, choose File > Open, select the first PDF, and open it. Repeat for the second. You can also select both PDFs in Finder and choose File > Open With > Preview. Apple notes that multiple files opened in Preview may appear in one window or in tabs, depending on your settings. For side-by-side viewing, you need two separate windows. Apple’s instructions for opening PDFs in Preview explain the opening options.

If they appear as tabs, drag one tab out of the window to make it a separate window. Apple also documents the Window > Move Tab to New Window command for detaching a tab. If you open the PDFs together again later and want separate windows by default, go to Apple menu > System Settings > Desktop & Dock and change Prefer tabs when opening documents from Always to Never. That setting affects documents across apps, so change it only if you want that broader behavior. Apple’s Preview window guide describes PDF tab behavior, and Apple’s window-arrangement guide documents separating tabs from windows.

Place one PDF on each side of the screen

With both PDF windows open, hover over the green window button at the top-left of the first window. Choose the left-side layout under Move & Resize. Then select the second PDF window for the right side if macOS prompts you to complete the arrangement. Repeat with the opposite side if needed. The menu names and available layouts can vary with your macOS version; use the left and right half layouts when they are shown. Apple’s guide to tiling windows on Mac describes choosing a layout from the green button or the Window menu.

You can also drag one window to the left edge of the screen and release it when the highlighted area appears, then arrange the other window on the right. If the built-in side-by-side layout is unavailable or gives too little room to read, resize both windows manually and drag them beside each other. macOS aligns adjacent windows as their edges approach. Apple documents both window tiling and manual alignment in its window-arrangement guide.

Navigate to the pages and make the comparison readable

Click the left PDF to activate it, then use Go > Go to Page or click a page thumbnail in the sidebar. Do the same in the right PDF. If both pages have a known number, matching page numbers is a useful starting point; if the revised PDF has inserted or removed pages, navigate to the corresponding content instead. Preview supports page navigation through the thumbnail sidebar and Go > Go to Page. Apple’s Preview viewing guide lists these controls.

For a fair visual comparison, set both PDFs to the same zoom percentage. Preview offers View > Zoom In, View > Zoom Out, View > Actual Size, and a percentage field in the toolbar. If sidebars take up too much room, choose View > Hide Sidebar in each window after navigating. Keep both pages at the same scale when checking layout, spacing, charts, or images; use a closer zoom when examining small text. Apple documents zoom and sidebar controls in its Preview guide.

A useful pass is to compare one category at a time: first headings and body text, then figures and labels, then page layout and footers. Keep your place by recording the page numbers or using a note outside the PDFs. This is a practical workflow suggestion, not a feature that Preview provides automatically: ordinary side-by-side viewing does not synchronize scrolling or report differences for you.

Know what Preview’s page commands do

Preview’s View > Two Pages option displays two facing pages from the PDF currently open in that window. It is handy for comparing a spread or checking how a single document flows across a page break. It does not place a page from a second PDF beside the first; for that, use two windows tiled next to each other. Apple documents Two Pages alongside Single Page and Continuous Scroll.

Preview also does not provide a documented command in this workflow to synchronize the page position or zoom between two separate PDFs, nor does it create a change report from ordinary side-by-side viewing. Treat the windows as independent: after scrolling or changing zoom in one, check the other and reset the view if needed. If your task is to identify changes across entire PDF versions, rather than visually inspect two particular pages, a dedicated comparison tool may be more suitable.

When you need an automatic change report

Adobe documents Compare Files in Acrobat Pro as a tool for comparing two PDF versions and generating a results document. Its settings can limit comparisons to selected page numbers and choose among document types, including reflowing reports and scanned pages. The results include a side-by-side view with highlighted differences. Availability depends on using Acrobat Pro; it is a different task from simply opening two pages side by side. Adobe’s Compare two versions of a PDF file guide describes the tool and its limits.

Where Wallo fits

If you are comparing PDFs as part of a larger Mac task, Wallo can help organize existing open windows and to-dos locally by goal, with keyboard focusing. The PDFs themselves still need to be opened and arranged in Preview or another app; Wallo does not add automatic window tiling, synchronized PDF navigation, or a PDF difference report.

For a quick visual check between two specific pages, open each PDF in its own Preview window, tile the windows left and right, go to the corresponding pages, and match their zoom levels. Switch to a comparison tool such as Acrobat Pro when the task calls for a generated change report across document versions.

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