hi Anita,
here have been several reports of similar behaviour since the recent OS upgrade.
Your next step is to restart your MacBook into Safe mode.
Choose restart in the Apple menu, The Mac will close all open applications, then shut dows. Shortly after getting to the dark screen, it will restart.
Press and hold the shift key as soon as you hear the startup chime. Keep Shift pressed until you see the Apple logo and a progress bar under it, then release the shift key and wait for startup to complete.
This will take longer than a normal startup as the OS calls several extra cleanup' routines. You'll also nice a degradation in video performance during this session.
When you see the log in screen, sign in as usual.
After signing in, you can try opening Pages and opening a document, then close the document and, pages, and do a normal restart.
More information regarding Safe mode is available here.
Regards,
Barry