There is a recent issue with Microsoft Outlook 2016, where you are unable to forward an attachment in an email due to the format showing as plain text. This was caused by a recent update release – KB4011626 – we do not recommend removing the update since it is a security update.
To workaround this problem, you can:
- Open the email
- Copy the attachment
- Forward the email
- Paste the attachment
This seems to be affecting Outlook on both Windows 10 and 7. Hopefully this will be resolved in the next round of updates