I am unable to help with getting Thunderbird to do what you want by itself. I use and recommend the add-on "AttachmentExtractor", which does an excellent job for me. I don't use all it's options, just the setting the folder to save attachments to, and its toolbar button which automatically saves out attachments to that folder.

Go to the Add-on Manager window (Thunderbird menu: Tools: Add-ons), and put "AttachmentExtractor" in the search box to find and install the add-on. After restarting Thunderbird to finish the installation of the add-on, go back to the Add-on Manager window, click on "Extensions" on the left side, then the "Options" button beside "AttachmentExtractor". Set all sorts of fun options (or the bare minimum).

If an "AE Extract" button doesn't automatically show up in the Thunderbird toolbar, then right-click the toolbar, choose "Customize". Find the AE Extract button then drag and drop it onto the toolbar where you want it.

Open Tools/Options/Attachments/Incoming and select the line for pdf Content. Click the Action drop-down and Delete Action, OK to close Options. Restart TB and next time you double-click a pdf attachment, select Save File, and see if the setting now sticks.

If not, reply here for instructions on how to check that the Downloads folder is correctly set.

no I am afraid that it still asks to select a folder rather than just saving it directly to the folder set in options/attachemets

If you open Tools/Options/Advanced/Config. editor and type downloads in the Search box, what do you see for these preferences:

browser.download.dir browser.download.downloadDir browser.download.lastDir messenger.save.dir

They should all have the value C:\Users\username\Downloads if that is the set folder. Right-click, Modify, and enter the path to the folder.

checked as requested

browser.download.dir - correct value browser.download.downloadDir - correct value browser.download.lastDir - this does not appear in the list messenger.save.dir - correct value

I have tried the add-on suggested by Bruce Johnson and it does what is required so I am not too worried if this proves to be a lost cause but it would be nice to find out what has gone wrong as it might help somebody else

Having tried a few tests, I find that if the Default Action is set to Save File, then double-clicking the attachment at the bottom left of the message does indeed save the file to the specified directory. However, if the attachment is right-clicked, Save As..., then the directory selection dialogue appears, as it should, no matter what the Default Action is. Same result if the Save All button at the bottom right is clicked. The confusion arises because if there is a single attachment, the Save All button appears as Save, even though the associated menu command in the drop-down is Save As...; the button should display 'Save As...'

So, I suggest you double-click an attachment and see if it automatically saves to the specified directory.