double-side printing: blank pages are not counted as even?

Solution 1:

Preview should normally print blank pages in a PDF document. They are still valid page objects. There is no setting in Preview itself to skip blank pages.

It's most likely that your printer has its own setting to eliminate blank pages. You'll need to check its configuration to see if such a thing exists and is on.

Solution 2:

I found the problem: "Use skip blank pages mode" is On by default, turn it off if you want to print blank pages.

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