pdf file linked in message is downloaded on android phone instead of opening to be viewed

I uploaded a pdf file to the library and put a link to it in my Constant Contact message. When one of my contacts received the message, the pdf file will open from the message on his computer but not on his Android phone. He receives the message ok, but when he clicks on the link Instead of viewing the file, it is downloaded on the phone. He then has to search for the pdf file on the phone and click on it to open it. The contact uses Chrome on both his computer and his phone. This problem may also affect other contacts who use Android phones to view their messages. Can anyone help?