After upgrading Thunderbird to version 91, the following issue occurred.
When creating a message, I attach a pdf file. When we try to open the attached file for viewing, I get an error:
The file “d: \ User \ Desktop \ test.pdf” cannot be opened because the associated helper application does not exist. Change the settings.
This problem exists only for PDF files, only for viewing when creating a letter. If I use a different profile in the same copy of Thunderbird, viewing the pdf there when creating a letter works without problems.
In the error console I can see the following entry:
Question: how to normalize Thunderbird - return the ability to view the pdf file when composing an email?