PDF download failing

I keep getting a message that my PDF download has failed. I have reduced the size of the file from 25 .4 mb to 15.3 mb, tried everything  suggested on your help line including the use of a different browser and computer using windows 8.1 without success. I have had no trouble before downloading larger like files. When I signed into my account I received a message that there was a download was available which I downloaded . It also failed with the message that a critical download has failed. could you please help me with this problem as I am on a strict time limit to get this dowload completed and the document issued. Thank You  Dennis Hawkes