If I understand what you want, Adobe Acrobat can do this. I am using Acrobat 7.0 Pro, but I think the standard version and some earlier versions can do this.

First you can convert each of your files to pdf format. Then you can assemble them into a single pdf document (using Create pdf from multiple files), then rearrange the pages. Finally, you can select "view face-to-face" to see two pages at once.