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From the github:

Another option is to compare the two files visually in a simple GUI, using the --view argument:

$ diff-pdf --view a.pdf b.pdf

This opens a window that lets you view the files' pages and zoom in on details. It is also possible to shift the two pages relatively to each other using Ctrl-arrows (Cmd-arrows on MacOS). This is useful for identifying translation-only differences.

Shifting the offset is very far from the experience of a side-by-side diff, and more useful for nudging the images to align them.

There is also an open-source/free version of this [1], which I use regularly. You can install it, e.g., in Fedora, with the ‚diffpdf’ package. It is no longer maintained but works very well, has a nice GUI with a side-by-side view, drag&drop support, and both text and visual modes.

[1] https://www.qtrac.eu/diffpdf-foss.html

I use BeyondCompare 5 for this.