Downloading files that promise "premium" accounts often leads to several negative outcomes:

: Files labeled as .txt or .zip containing account info are common vectors for Trojan viruses and keyloggers . These can steal your own personal data, including your main Steam password and financial information.

Instead of risking your security, use these official methods to expand your library: Scam: Account Sellers and Traders - Steam Support

: Most "free" account lists consist of accounts hijacked from legitimate users. Using them supports account theft and often results in the account being locked or banned by Valve shortly after you gain access.