A .7z file is a compressed archive created using the format, known for its high compression ratio and strong AES-256 encryption capabilities. Technical Summary of .7z Archives
It supports high-level encryption. If this file was sent to you, it may require a password to extract. DocumentsForLilly.7z
You can open and extract it using free tools like 7-Zip for Windows or PeaZip for cross-platform use. Security Warning DocumentsForLilly.7z