Hello There all So I recently installed Win11 and Tbird 115.7.0 My issue is this: When I double click a PDF in a received email it opens up in my default PDF reader (Foxit) so it's all good. When I'm composing an email and add a PDF I like to check to see that I'm sending the correct PDF attachment so I double click and it won't open, I get this message (Attached Image) I went to Tools/Settings/General/Files&Attachments and PDF (Foxit) is set as the default so all good So again Inbox messages opens PDF's no problem Composing messages won't open PDF's I used to do this all the time on Win10 and it worked perfectly See my settings in image 2 Thanks In Advance :-)