Batch convert 4 PDF pages to one PDF page

I have a PDF with 100 pages. How can I make a new PDF that displays 4 pages on one?

I know that I can do it with Chrome by printing the PDF to new PDF and change this in the options. But I want to make it for a lot of files and put it as a script.

The most simple solution I recall to memory is to use pdfnup

pdfnup is written and maintained by David Firth as part of the PDFjam package

Use
If the original name for the file is MyFile.pdf the syntax can be something similar to

pdfnup MyFile.pdf --no-landscape --nup 2x2 --column true

and it will create a file named MyFile-nup.pdf. After you checked and chose the right options from the commandline you can include it as command in your script.

This runs on Unix-like OSes (or Windows with Cygwin and the tetex-extras package installed). It requires that pdfpages and pdfTeX also be installed (and other packages for specific cases). See details in the pdfjam link under References, below.

Note
The use of imagemagick should present problems related with the internal conversion in images in the process pdf---> images --->pdf. TO have an idea see "Convert PDF to image with high resolution".

References