Inconsistent PDF link behaviour

Hello all,

I recently built a WordPress site for a catering company and figured the best way to go for displaying their menus would be to simply add a link to a PDF file, as they change them pretty much every month.
When I built the site I tested it on both a PC and a mac and in all the major browsers, without any problems downloading the PDFs but now my client called me complaining that they can’t view or download the PDFs from the site and that they had people calling them with the same problem, saying the PDF “could not open or appears broken”.

I really can’t see what have gone wrong nor if this could be caused by my code. Has any one else had this same problem or any ideas of what may have caused it?

Here is the site (click on the images to view the PDF)

Any help is greatly appreciated!