For some users, and particularly those that upgraded from the PDF Pro 10 trial, a black background appears for all PDF files opened with PDF Pro 10. This is a known issue with the software.
It appears that the watermark that is placed automatically in the trial version is causing this issue. In order to change this, simply select the black background using the "Select" tool and press "Delete" on your keyboard. This should eliminate the problem.
If this does not help, make sure to download the latest version of the product using this link: www.pdfpro10.com/trial/com. Make sure to uninstall and then reinstall PDF Pro 10 and activate it using the license key that you purchased. We have fixed this bug with the new version of PDF Pro 10, and this should no longer be occurring.