Why do PDF documents open with ImageMagick?

Query shows evince is my default handler.

But, double clicking a pdf file opens ImageMagick. A pdf file's Properties shows ImageMagick as the default handler.

Why is this happening ?

_{After answering the why, also tell me how to solve it using the terminal. I am very fond of using terminal. I tried sudo xdg-mime default evince.desktop application/pdf, nothing changed, even after logging out and back in.}

You might find this is a more clear answer that worked for me in Ubuntu 15.10:

• edit the file ~/.config/mimeapps.list

• just remove the lines that associate PDF to imagemagick in the file:

  image/pdf=display-im6.desktop
  image/pdf=display-im6.q16.desktop;display-im6.desktop;
  

The thread where I got this answer that worked for me is here: Unable to restore Envince as default pdf viewer