Hi gale.stewart, a possible solution is as follows, I have tried this solution on elementary OS, which is based on Ubuntu. First and foremost I think that you should re-install Adobe Reader, since I'm worried what you state about acroread being located in the bin folder. Close Thunderbird. '''FIRST;''' These are the steps for reinstalling Adobe Reader; Source: FOSS Linux, How to install Adobe Acrobat Reader in Ubuntu and Linux Mint); QUOTE STEP 1: Launch ‘Terminal.’ STEP 2: We need to install certain 32-bit libraries for the Adobe Reader to work flawlessly. Enter the following command. sudo apt install libxml2:i386 libcanberra-gtk-module:i386 gtk2-engines-murrine:i386 libatk-adaptor:i386 STEP 3: Enter the following command to install gdebi package installer. sudo apt-get install gdebi-core Enter the root password to complete the gdebi installation. If it doesn’t prompt for one, nothing to worry. Wait for the installation complete notification in the Terminal. STEP 4: We shall install Adobe Reader now. Copy and Paste the following command in the Terminal. Use the right-click context menu to paste. Ctrl +V won’t work in Terminal. This command will download the pdf installer Debian binary from Adobe’s official servers. wget ftp://ftp.adobe.com/pub/adobe/reader/unix/9.x/9.5.5/enu/AdbeRdr9.5.5-1_i386linux_enu.deb STEP 5: Use the gdebi command to install the downloaded .deb binary package. sudo gdebi Adbe*.deb STEP 6: Enter the root password when prompted. UNQUOTE Open Thunderbird AND THEN doubleclick on a pdf attachement , and you should get a menu asking you which application to use (What should Thunderbird do with this file?" , you may or may not see acroread/Acrobat Reader or other app chosen, if not click on the name (or empty) drop down list and chose one in the list Other.. or eventually click on All.... '''Then eventually SECOND''' If you do not see acroread/Acrobat Reader, then we need fix this too. In order to do this (you should not need to close Thunderbird) STEP 1: Launch ‘Terminal.’ STEP2: Use the following command "sudo nano /usr/share/applications/AdobeReader.desktop" (quotes are only illustrative, do not use quotes, you may have to provide the roor password) ** STEP3: Where it is stated "Exec=acroread" change to "Exec=acroread %F" (aka adding "%F", quotes are only illustrative, do not use quotes) STEP4; Press ctrl-X, then Y (save modified buffer) ** I suppose nano is installed, you may use any other preferred text editor, of course You should now be able to choose acroread/Adobe reader in Thunderbird when you open a pdf file and make that choice your preferred choice. I hope this will solve your problem. All the best from Stockholm.