Would there be a way to crop something  

I'm in the process of taking square pictures a lot of CD booklets to turn them into PDF.
When I tried it on Mac, it's leaving a lot of blank white space on top and bottom.
When I tried it on Windows using "Print to P it's leaving blank space on left and right.
When I check the "Fit picture to Frame", the blank space on left and right is gone but some portion of the picture is cut off at top and bottom.

Is there a way where I set it up so that when I make the PDF out of pictures, I can choose a custom dimension so that I don't have to crop it after making the PDF?

The old Paint/MSPaint program can do it, Select and Crop. Can also Resize. Check Start, W, Windows Accessories to see if still there or search the Tutorials section here, may be something there about getting it back.

You can do it in LibreOffice Draw.
Make your own format size.
Page -> Properties.
Format -> User.
Set a width and height of equal size and you got a square format.



Add your covers per new page.
Export as PDF.