If you get a message when trying to add the Screenshot Reader Chrome extensions that shows that it is blocked by administrator there are likely restrictions on adding Chrome extensions on the domain your account is setup with.
Chrome administrators would need to refer to following the instructions in this Chrome for enterprise Help article Manage Chrome apps by organizational unit for allowing the extension.
Screenshot Reader can be allowed by the extension ID and URL:
ID: enfolipbjmnmleonhhebhalojdpcpdoo
URL: https://chrome.google.com/webstore/detail/screenshot-reader/enfolipbjmnmleonhhebhalojdpcpdoo