The QuickBooks PDF component missing issue refers to a situation where QuickBooks encounters difficulties in generating or sending PDF files, such as invoices or reports. This issue usually arises due to a missing or corrupted component called the "QuickBooks PDF Converter," which is responsible for creating PDF files. To resolve this problem, users can reinstall the QuickBooks PDF component by running the QuickBooks PDF & Print Repair Tool or manually reinstalling the component through the QuickBooks installation process.