To make a booklet-style PDF, use this:

pdfjam --landscape --signature 4 --paper letter --booklet true '(half-leffer pdf)'

The PDF will use only the margins specified in the document. Please note that if you're printing pages with background colors/styles that cover a whole page, you'll want to choose a "US Letter - Borderless" or similar option from your print menu. (Keep in mind this may cut off the edges slightly - though this is usually preferable to having a white border around the document.)

Besides that, make sure you're printing in landscape orientation and double-sided with long-edge binding. Not convinced the partially upside-down output PDF makes sense? Just try a few pages with those settings!

If you intend to fold pages, make sure you do so in the correct direction - the smaller page number on the earlier half of the sheet should be on the outside after folding.

If you're printing page signatures (chunks of pages folded instead of sliced down the middle), you'll want to specify the number of pages per chunk as the argument to '--signature', and remove the options '--booklet true'.