The HP OfficeJet Pro 8620 printer driver unavailable error stops you from printing and performing functions like scan and copy. If you encounter this error, then you should update your Windows OS by following the steps mentioned here. First of all, click on the Search Bar button and enter the word “Update.” The Search Bar will display a list of possible options related to your query. Find and select Windows Update and click on the Check for Updates button. Windows will begin checking for available updates and install them automatically. After the process is done, restart your PC and print a page from it to see if the HP OfficeJet Pro 8620 driver unavailable issue has been resolved.