[LOCKED] iPad Pro cannot open pdf-files

Hey you all,

my iPad pro 12,9'' cannot open pdf files. When I select the file, which is supposed to be opened, the select screen disapperas (as normal), but after that the app does nothing. The file was not opened and I am back looking at the start/ home screen of the app at the list of files, which were opened at last.

I hope that somebody maight help me.

Thanks

Kilian