There is an issue with Chrome Browsers that is causing the "initial" load of PDF files to fail. It is all over their forums and all "fixes" deal with instructions to the actual end users. There is no fix that a webmaster can do from the server end so far.
We usually find Firefox is the best browser for WordPress sites, but Chrome and Safari usually perform very well.
If you see this message DO NOT click Reload
Instead you have to first install the Chrome Extension called PDF Viewer.
Then after it is installed you will still probably need to reload it as it will probably start loading then just stop.
Right-Click in the dark area to the right and THEN
click the Reload link that appears in the drop down box.
This is something outside of our control. Sorry about the issue,