Hope you are doing well. Sorry for your experience with Acrobat DC and the delayed response.
Would you mind sharing the screen recording of the workflow you are following for better understand?
Also, please share the below pieces of information:
1. The application version of Acrobat DC;
2. The Operating system and its version;
Please try repairing the application by going to Help-> Repair Installation.
You may refer to the given thread which has answers to a thread with an issue similar to yours:Solved: Can't sign document in Adobe Acrobat Reader DC
Look forward to hearing from you.