I was opening an file and had a choice of 3 apps to use. I pressed always for pdf but want to have the choice of others again how do I change?
It seems that you have enabled a specific application to use it as a default. No worries since you can reset it through Settings> Apps> 3 dot menu> Reset App preferences.
If not, please perform Reset Settings to set the settings to default(It will not affect any data in your device) through Settings> General Management> Reset> Reset Settings.