Unable to change default viewer for pdf docs

[Condobloke]

1) Open your Home folder, then press ctrl + H (this shows hidden files/folders, which all begin with a " . ")
2) Open the hidden folder .config
3) Inside that open the file mimeapps.list with your simple text editor
4) Find the line that reads either a) image/pdf=display-im6.desktop -OR- b) image/pdf=display-im6.q16.desktop
and delete it. [Basically you're looking for a line that has both "pdf" and some form of "im" in it. The numbers may be different due to what version of image magick is on your system. Also, it may or may not have "image" next to pdf.] Save your changes and close the file. Now when you open a pdf it should open with Document Viewer.

Brilliant advice @ron.alan

To give this situation more perspective......I now run Linux Mint 21.3
I have imagemagick installed

My defualt app for opening PDF's is Document viewer.
There is NO conflict. No need to alter the "" image/pdf=display-im6.desktop -OR- b) image/pdf=display-im6.q16.desktop"" lines...WHY ?.....because there has obviously been CHANGES either in Linux Mint itself or in IMAGE MAGICK itself. I have never liked the app....mainly because they used to BUNDLE other crapware with their app. That is not in the spirit of Linux....it takes away CHOICE>

SO. to summarise for @UpNorth ....when you get around to upgrading to LM21.3 the problem will no longer exist.

I actually have two iterations of image magick installed now with no harmful side effects

 

[ron.alan]

Brilliant advice

I can't take the credit. I found it on Mint's forums.

 

[Condobloke]

Take the credit, anyway ! Nobody else offered it/went to the trouble to find it.