Chrome, Firefox, Safari have their own built in PDF viewer (IE does not). That maybe why it's not working.

The problem is that third party PDF viewers doesn't support all form's features. The PDF needs to be downloaded locally and filled out with either

Adobe Acrobat, Adobe Reader or the Adobe Reader Mobile.  Also Android version of Reader

Make sure that you download it and fill it out with a Adobe product which will support all PDF form's features.
 (The above came from Adobe Forms Central Forum 8/2013)

Also if your behind a firewall  and you aren't allowed to except a unknown file you may have a problem.

1.      Download Adobe Reader it's Free and available for most OS (PC, Apple, Droid, I Pad) http://get.adobe.com/reader/

2.      Try "Save As" file to computer and then open it in Adobe Reader.

3.      In firewall situation you may be ask to Ok that you trust this file/ link if you select "Yes" a pop up box will show it's uploading and a "Thank You for submitting" will show up it should go though and if "No" you will need to save a copy and email it in.

4.      Try Different computer

I hope this helps.