While logged in, edit your page (/quick-guide-to-corporate-photography) and click on the “Text” editor. Remove the class="single_photoswipe" from the <a> link tag. This will allow your PDF to open without the special handling provided from the Photoswipe Masonry Gallery plugin.

Here’s a step-by-step video I created that (1) successfully recreates the error you’re experiencing and (2) outlines how to fix it: