PDF expert removed it self from my ipad I need to restore my documents

When you delete an app, that will remove all its data as well. Even by downloading the app again, the data is gone unless the app was used to store data on icloud (most apps do not use icloud to store their data, the data is stored on the device and is deleted when the app is deleted). So it all depends on the app and whether you opted to store whatever PDF files it had onto icloud (if it has that option).

If you did store the file(s) on icloud, then the app also has a way of downloading its data from icloud - you have to figure out how that works, as each app has its own menus and capabilities.