comic book - need to double dimensions on each page

I have a pdf of a 26 page comic book.  Each page is about 900 pixels wide.  I need to change the document so that every page is more than 1800 pixels wide (and proportionate changes in the length too).  I can't figure out how to do this. 

Let me clarify by saying that I mean the images on each page.  The images (each one a page of the comic book) are about 900 px wide now, and I need to increase them to 1800 px wide with proportionate changes in the length.  The vendor I am working with only accepts art if it is minimum 1800 px on the smallest side.

Please advise.  Thanks!