If you have access to a WebDAV server, you can transfer documents between the server and your iOS device. You can also open and edit them on the server.
Tap the Files app on the Home screen, then tap Browse at the bottom of the screen to see the Locations list.
If you don’t see WebDAV below Locations, tap Edit in the top-right corner of the screen, tap WebDAV to turn it on, then tap Done.
Tap WebDAV in the Locations list, then tap Connect to WebDAV Server.
Type the server address and your user name and password, then tap Sign In.
After you sign in to your WebDAV server, you can open and edit files on the server without signing in again. You remain signed in to the server until you tap 
next to WebDAV in the Locations list.
Do one of the following:
Copy a file from the server: Tap the file on the server. When the transfer is complete, the file appears in the document manager. Tap the file to open it on your device.
Copy a document to the server: With the document manager in browse view, tap Select in the top-right corner, tap the document, then tap Move at the bottom of the screen. Tap WebDAV, then tap Copy in the top-right corner.
Open and edit a file: Tap the file. When the transfer is complete, the file opens and any edits you make are synced back to the server.