Norton Safari Plugin Corrupts pdf files

I recently installed Norton Security 6.1 on several Mac machines; two IMACs, a MacBook Pro, and a MacBook Air.  All Macs are running Mac OS X Yosemite.  I read a lot of medical journals online and download pdf files for my article library.  After installing Norton Security and the Norton Safari plugin on all my machines I began having problems viewing pdf articles from two journals from the American Academy of Allergy and Clinical Immunology, the Journal of Allergy and Clinical Immunology, and the Journal of Allergy and Clinical Immunology In Practice.  The files were corrupted and unreadable in the browser and although I could save the articles, when I tried to open them in Adobe Acrobat Pro I got the message that they were damaged files and could not be opened.  I discovered that by turning off the Norton Security plugin in the Safari browser, I could read the files normally in the browser and save them and open them and mark them up successfully in Adobe Acrobat Pro.  I used Norton Security to scan the files that were successfully downloaded and opened again in Acrobat and no viruses were detected.

Interestingly, I have had no problems with other journal websites in reading and saving their pdf files with the Norton Security plugin being active.