The "bit.ly windows10pro.txt" phrase refers to a viral, unsafe method using a batch script to illicitly activate Windows 10 Pro by exploiting Key Management Service (KMS) through untrusted servers. Using these scripts poses severe security risks, including malware injection and ransomware, by requiring users to disable antivirus protection and grant administrative privileges to unknown code.
Should you encounter a bit.ly link pointing to a windows10pro.txt file, never click it directly in your OS. Use safe analysis methods: bit.ly windows10pro.txt
A short paper explaining that: