How to Restore Riched20 DLL

1. Open your default antivirus program if you have one installed and run a full system scan. Error messages related to .dll files are often related to viruses or malware, so this is a good first step. If your virus scan catches something, take the program's recommended action to delete or quarantine the infected files, then see if the problem persists.
2. Restore your system to a restore point from before you experienced problems related to riched20.dll. To do this, click 'Start,' look in the 'Programs' list, then in the 'Accessories' folder, and finally in the 'System Tools' folder. Click 'System Restore.' On the 'System Restore' screen, indicate that you want to restore your system to an earlier point and select a valid date off the calendar from before you experienced problems. Click the 'Restore' button and wait for your computer to complete the restore process, then see if the problem persists.
3. Reinstall your Microsoft Office software, or if you prefer, just reinstall Microsoft Outlook. To do this, insert the original installation disc in your CD-ROM drive, wait for the installation program to auto-launch, and follow the on-screen prompts to reinstall Outlook or the entire suite. Outlook is the program that relies on riched20.dll the most, and a duplicate of the file is included with the installation files of Outlook.
4. Download and install the Microsoft security updates that affect riched20.dll. A link to the download location can be found in the Resources section of this article. These updates correct a vulnerability in Microsoft RichEdit that may have contributed to your problem in the first place. When you go to download the updates, make sure to download one for your operating system and one for your Microsoft Office suite, and make sure you select the right updates for your version of each product. Double-click the downloaded files and follow the on-screen prompts to apply the updates.