but here's what I do to turn the GPS on and off:

Tap Tools. Tap Settings. Scroll down to Location and tap Location. Make sure Location is turned on (slider switch at the top of the screen). Tap Mode (appears below slider switch). Tap either High Accuracy or Device only. That turns the GPS on. (To turn the GPS off, go to Mode then tap Battery saving.)

Once the GPS is on, open PDF Maps. My opening screen is a list of maps. Tap the map you want. The map should appear on the screen. There is a GPS icon at the top left corner above the map. Tap the GPS icon. (Note: PDF Maps does not automatically acquire a GPS position. You have to tap the GPS icon to get the app to do so.) Once the app has acquired a position, it will be displayed as a blue dot on the map. (That's assuming your location is on the map being displayed on the screen.)