Internet Explorer → Options → Advanced → Do not save encrypted pages to disk
If the above options are enabled, PDF reports cannot be displayed. As a
workaround, disable Do not save encrypted pages to
disk.
Verify whether the Internet Explorer Enhanced Security
Configuration Windows component is installed.
If so, reports sent as email attachments cannot be opened directly from the
message. As a workaround, remove Internet Explorer Enhanced
Security Configuration or save the attached
*.MHT file to a local folder before opening the
report.