We have been using this script from cad-notes.com for some time now:
http://www.cad-notes.com/open-autocad-drawings-as-read-only-using-right-click-from-explorer/
Issue: We just upgraded to 2019 but the script still opens autocad files in 2017.
-At this point we do still have 2017 installed on our machines (so this may be a non-issue when that gets removed).
-I have set all autocad related files to open in 2019 by default.
-Opening autocad files normally through windows explorer does open them in 2019.
-The script file still "reverts" to 2017.
-I was having an issue getting .dwt files to default to 2019, but when I fixed that the readonly script started defaulting to cadworx 2017 for some reason 
Does anyone know a fix for this, or will it solve itself when we get rid of 2017?
Sorry, I would post to the original page where the script was shared, but I don't have an account with that site.
Thanks.
