If your files look blank when you open them after you update PDF Expert, first of all, please try rebooting your iPhone or iPad.
If it doesn't help, please send us logs - we're happy to help you personally:
*The logs you will send us may contain sensitive personal information, so we encourage you to review them before sending them to us. We will, of course, treat logs as confidential information, never share them with third parties and retain them according to our Privacy Policy.*
Read next: Annotation tools do not work