Thank you for the reply.
Not sure what went wrong but it now works! So far so good.
DT3 appears to display different file types at different magnifications. Is it best to set the text at (say) 18pt or the usual 12 pt with a magnification of 150% Would this setting then ‘stick’ or would I need to reset the magnification each time? I have a feeling that the setting in the prefs may over ride anything in the template.