Use Advanced PDF Tools to increase pages margin to PDF files

Hello,
I've got your advanced pdf tools 3.0. I really, really need to know how to scale some PDFS. My originating PDFs are already cropped to size, meaning, they have no white space around the actual graphics. Most of them are about 7 inches wide. I need to be able to scale them, proportionately, to about half that size. I've played with -x and -j, but, nothing works yet.
I'd appreciate any help.
Thanks,

===================================

You can use “Increase pages margin” option to increase the margins, please refer to following screenshot,