You've intercepted a transmission vital to navigating through the Cyber Nebula. The message is locked in a high-security encrypted PDF file, and the encryption key is a combination of personal identifiers lost in the space-time continuum.

Another transmission intercepted by your team member has revealed the following information:

• Password is a blend of two elements: the first four letters of a user's name (lowercase) fused with their date of birth in the DDMMYYYY format. For example, for user John born on 15th August 1947, the password will be john15081947
• User name list for all suspected users:GitHub User List
• User's snap clicked sometime in 2023

Remember, your skills in decryption and deduction are crucial for the survival of your mission in the vast, uncharted territories of cyberspace.

Objective: Decrypt the message to continue your journey through the cosmos of code!