Issues when highlight text on iPad

Hi 
I have just downloaded Acrobat Reader(free version) to my iPad. When I try to highlight a text by selecting with Apple Pencil, the keyboard pops up and the PDF freezes. Any action cannot be taken after this happened but only to manually close the application and re-open. I have tried other features, underline, strikethrough, when the keyboard automatically pops up when I try selecting a text then freezes.

Please assist