By default XenForo gives all non-image attachments the MIME type of 'application/octet-stream' - this means that attachments such as .pdf and .txt files will act like binary files, and not be opened by the browser (instead they will be downloaded, and you have to open the downloaded file).
- Compatible XF Versions:
MetaMimeType is a small patch to replace the MIME type on .pdf and .txt attachments files so they display correctly.
The types are set in the options as a simple list of extension,mimetype, extension,mimetype, etc...
So you could add more.
MetaMimeType: View PDF Attachments in-browser 0.2a
Alters the MIME type of .pdf and .txt files so they display in the browser instead of downloading.