In case the file can't be opened and instead you see the message about it being corrupted, these are the first aid steps for your PDF:
Restart your app by clicking Force Quit in Apple Menu or on the app's icon in the dock.
After this, launch the app again and check if the file can be opened.
Try opening the same file in the Preview app and after this check if it opens in our app - opening your corrupted file in the system viewer might trigger the file to be rendered again because of the same system component we're using. If the file can't be opened in Preview as well, drop us a line at firstname.lastname@example.org and send us the affected file if possible - we're happy to help personally. If the file is too big to be sent over email, you can upload it to any cloud storage and share a link with us or use a third-party storage service like WeTransfer.