Not being able to input anything from the keyboard (keypad) into libreoffice is a generic problem, and may be due to any of a variety of reasons. We need your help to complete this page in order to help users quickly overcome their problem.
Input method configuration
If you use any input method like ibus, fcitx, etc, check its configuration.
Turn off completely the input method, restart your session with the input method off, and see if it solves the input problem with libreoffice. If it does, then check further the input method installation and configuration.