Hope you are doing well and sorry for the trouble. As described, you are having problems with opening Acrobat Reader DC. It is asking for a document password.
Is it the application (Adobe Acrobat Reader DC) that is not opening or is it the document that is not opening and asking for a password? Please try to open a different PDF document and check. Also, please share the screenshot or a video recording of the issue for a better understanding.
If its a document that is password protected and asking for a password to open, please enter the correct password to open it. If you have forgot the document password, you may need to create a new PDF from the original source file or contact the author/owner of the PDF.