The maximum file size allowed is 4Mb. You will need to reduce the PDF file size or use a Compressed (Zipped) Folder.  

To Zip a File:

  1. Locate the file or folder that you want to zip.
  2. Press and hold (or right-click) the file or folder, select (or point to) Send to, and then select Compressed (zipped) folder
  3. A new zipped folder with the same name is created in the same location.

To reduce a file size:

  1. Open the PDF
  2. Click File >Save as Other
  3. Select Reduce Size PDF 


Zip File:

Compress PDF Online:

More information: