Hope you are doing well and sorry for the trouble. As described you are unable to use fill and sign function as the text is greyed out and you cant insert test into the PDF.
- Is this a behavior with a particular PDF file or with all the PDFs? Please try with a different PDF file and check. If the file is stored on a shared network/drive please download it to your computer first and then try filling it out and check if that helps.
- What is the version of the Adobe Acrobat Reader DC you are using? To check the version go to Help > About Acrobat and make sure you have the latest version installed. Go to Help > Check for Updates and reboot the computer once.
Also, please try to repair the installation (Win Only) from the help menu. Go to Help > Repair Installation and check