Hi, welcome to iPF!
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If you tell us, which way you receive PDF files, we'll certainly be able to help you use your device.
If you receive photos via email, the usual way to view them would be to tap them so you get a preview:
Tap to download would be your choice here.
If it is already visible, then tap and hold on the photo until this appears:
Here you can save the photo to your Camera Roll (Save Image), email it, and if you slide sideways, there will be the option to Open in..., which, when chosen, will show all apps that will work with the picture.
Hope that helps.