I hope you are doing well, and thanks for reaching out.
Could you please share more details about the issue? Are you unable to open a password-protected PDF file on a mobile device? Is it an Android or an iOS device? If you have forgotten the password for the PDF, you cannot open the file, and the Acrobat Reader mobile app does not have any settings to access such PDFs without the password. If you own the PDF file and have access to the source file used to create it, you can recreate the document without password protection. See this article to learn more about opening PDF files on an Android device: https://www.adobe.com/devnet-docs/acrobat/android/en/openfiles.html
To open a password protected file, you must know the password. If you are not able to open the PDF, you need to double check if you are putting the correct password.