What you will see
Camera make and model, lens, exposure time, aperture, ISO and focal length; the date and time the photo was taken and last edited; the software used; author and copyright fields; serial numbers where the camera records them; and the GPS position, altitude and direction. Fields that can identify you or a place are highlighted.
Where the GPS position comes from
Phones write the location into a photo when the camera app has location access. On iPhone that is Settings → Privacy & Security → Location Services → Camera; on Android, the camera app's own settings. Turning it off stops new photos being tagged - existing ones keep their location until you remove it.
How your files stay private
Most free converters upload your file, process it on their server and send the result back - so a copy of it passes through somebody else's machine. This page does all of the work in your browser instead. The files you choose are read into memory on your own device, processed there and handed back as a download; none of their contents is transmitted. You can switch off Wi-Fi after the page has loaded and it keeps working.