I find myself needing to take a PDF, output it at a specific size, and have the result offset to the top right hand side of the screen. To achieve it, I needed a few new switches to my good friend PDFJam, so I thought I'd share my command!
pdfjam --suffix converted --papersize '{1920px,1080px}' --scale 0.4 --trim "-6cm -1cm 13cm 8cm" slides.pdf
The --suffix is instead of giving an output filename, whatever you feed in ends up with the suffix in its filename. This is very handy because I use this command in a script and only need to pass in one variable. The --papersize isn't a switch I have used before either but you can set exact sizes for the final output which is nice. The --trim switch can also be used to set --clip=true to remove the trimmed space from the document if desired.
I find PDFJam a very handy tool but with not nearly enough blog posts and code snippets around, so I'm dropping my command for future reference (yours as well as mine!).