If you mean attachment, then this is literally a file attached to your email message, which requires the corresponding application to open it on your computer. Which application, that depends on the type of attachment. E.g. you'd open a PDF file with Adobe Reader.

If you mean links in the message body, then you need to click the link, which would open in a web browser.

Hi, New to TB. Get an email with PDF file attached. Double clicking the button at Bottom LH corner does not open my pdf reader and present the result for reading. Can save the attachment Bottom RH then go into windows "File explorer" and open it OK from there. Yes a work around BUT a horrible nuisance when my old "pegusus" email client did it easily.

Somewhere is the setup it asked me for the name of my PDF reader, BUT if TB cannot make use of the info frustration continues. Thanks for any help.

Hi, New to TB. Get an email with PDF file attached. Double clicking the button at Bottom LH corner does not open my pdf reader and present the result for reading. Can save the attachment Bottom RH then go into windows "File explorer" and open it OK from there. Yes a work around BUT a horrible nuisance when my old "pegusus" email client did it easily. Somewhere is the setup it asked me for the name of my PDF reader, BUT if TB cannot make use of the info frustration continues. Thanks for any help.

First rule of forum etiquette is not to ask a different question on someone else's post, even if it's related. Please go to https://support.mozilla.org/en-US/questions/new/thunderbird/form and post your question there.

OK Moderator. Tell me how my question is different to the subject of this discussion. You encourage us newbies to read the existing stuff first then send me "do not do it here message."

Thanks for your bureaucratic thinking. Why bother reading the existing stuff if this is your response. You will notice that the solved reply did not solve my problem.

Tell me how my question is different to the subject of this discussion.

You will notice that the solved reply did not solve my problem.

Looks like you answered your own question.