Hello JesperAsking,
Good day!
Thank you for posting to Microsoft Community. We are happy to help you.
This problem occurs when the software that the recipient is using does not support certain message formats or certain features that are included in the email message.
1. Are you using Internet Explorer or Outlook to send the emails with PDF attachments?
2. Did you make any changes to the computer prior to the issue?
- May i know the recipient outlook version and which window is using.
- Please send the same email with PDF attachment to another account (if you have other account) and use that account to forward to the affected account. check if the issue persists
If it is possible, you may run the following fix it on the recipient computers and check if that helps.
‘When you run an .exe file on a Windows Vista-based or Windows 7-based computer, the file may start a different program’
http://support.microsoft.com/kb/950505
Please get back to me with the information above, it will help me to find some work around for you
Please get back to us with necessary information, we’ll be glad to assist you further.
Appreciate your patience and understanding and thank you for your time and cooperation.
Sincerely,
Eben Ezer Tres | Microsoft Community Moderator