I think pdfposter is just the program i need for this, but I cant't get it working. I just don't know the correct command to tell it to turn my 93 upright pages into 186 wide pages, each page split in half.

and the google-link didn't help much, i'm afraid, the first link is nothing but a downloadlink for the software, no guide or sth. there. I have it already installed, so I didn't need a dl link...

btw: Does pdfposter work correctly with multipage PDFs? i think so, but since i don't know the command to get it working, i can't check it