Hi Danny,
1. Does the issue occur while opening specific .pdf file or all?
2. Have you installed any third-party pdf reader software?
You may face this issue if apps are not updated or if file is corrupted. Follow these troubleshooting steps and check if it helps:
Step 1: Run the **Apps troubleshooter**. This tool can automatically identify and fix some problems with apps.
Note: The troubleshooter automatically fixes some issues that might prevent your apps from running, including suboptimal screen resolution and incorrect security or account settings.
Step 2: Please go through the following link for troubleshooting further if the troubleshooter does not help:
**http://windows.microsoft.com/en-us/windows-8/what-troubleshoot-problems-app**
Hope this helps. If you need further assistance with Windows, let us know and will be glad to help.