There is a setting in Calibre where you need to set to allow the conversion of AZW (Topaz) files. It's not a plug-in I don't think. That setting must be set. I can't remember what part of Calibre is it in.
I just came across this link from Calibre that discusses Topaz files.
https://www.mobileread.com/forums/sho...paz+conversion
Are we sure it is a Topaz file?
I did a search for Topaz in the Calibre forum and came up with this results page. Maybe some of this can help. Make sure you have the latest version of Calibre and the latest version of the tools.
https://www.mobileread.com/forums/sea...archid=6767272