I have a set of HP printers, both at home and at work, that have this annoying feature of only allowing scanning (reliably) to 8½x14", with the only possibility for smaller documents to adjust scanning margins to be adjusted by "hand" (mouse precision, tiny preview rectangle) without any feedback on the resulting output size. In other words, I never get exactly 8½x11-inch scans, thus I always overshoot the height a bit and then trim back to the US Letter format.
With an older version at work (perpetual, one-time-fee licenses of Acrobat X I think), I never had a problem. With Acrobat DC (Pro), however, it just doesn't work–or rather, trying to crop to a predefined format just doesn't do anything.
Now, to be clear, I'm not trying to scale the document, whether up or down, I'm just trying to crop it down. Here are the steps I use:
Select the Scan & OCR toolset (pardon me if it's not the exact words, my installation is in French)
On the tool bar that appears, select the Crop tool (icon of a sheet with cropping marks)
Select an area of any size (it doesn't, shouldn't matter)
Double-click on the created crop area
On the dialog that appears, I select as predefined page format "US Letter" and choose to apply it to all pages (I have only one).
BUT, once I click on OK, the dialog box closes and no cropping occurs.
If I was to keep the previously-selected area for cropping, then Acrobat would process the page/document rightly so. But, for reasons unknown, selecting to crop, say, a 8½x11.7-inch document to exactly 8½x11-inch seems just out of reach, and so far impossible