I'm not ware of any adobe reader addon for Thunderbird. There is an Adobe Reader plugin to be used with Firefox browser. Adobe Reader is a free program for viewing and printing PDF documents. It includes an Adobe Acrobat browser plugin for displaying PDF documents within Firefox and other Web browsers. Tools > Options > Attachments > Incoming tab Under 'Content type' do you see: * 'Adobe Acrobat document (application/pdf: .pdf) what action is set? * click on the set Action to see a drop down box and select Adobe Reader * click on Ok to save changes. If it is not listed: * In Thunderbird, * select the email with pdf attachment, * right click on the attachment and choose Open. * A small window opens asking what to do with the file. * choose 'Open with' and select 'Adobe Reader' * select to 'do this automatically for files like this from now on' * click on OK