I made a program in Eclipse (on Mac) with a main method and class (which I called run). This program uses the pdfbox library which I imported and added to the build path. I am able to export this as a runnable JAR file on my computer that works fine. It seems to work on other Mac computers, but not on Windows. 
I asked a friend to copy the individual Java files over and the only error he had was that it couldn't find the pdfbox library, so I think the error is something with the library when it's exported, I'm just not sure exactly what. Any help would be greatly appreciated!
Here's a picture of the project in package explorer in case that helps.
 
    