While composing new message window and opening the attached pdf file to check whether right file attached (from email composing window) an error occurs '''pdf could not be opened, because the associated helper application does not exist. Change the association in your preferences''', but, I can open the pdf files (same email or other drafted emails) from "draft folder, after sending and accessing it from Sent folder and even from Inbox folder " which have pdf file attachment, in the system adobe reader. But when I change in default program settings to - "view in Thunderbird" it opens in Thunderbird (opening from composing window too), but I need to view in adobe reader. Using Thunderbird 115.18.0 (64 bit) Supernova in Windows 7 - 64 bit. Any ideas or solution anyone have?