Use the official 7-Zip utility (free and open-source). Alternatively, you can use WinZip or Unzip One .
A .7z file is a high-compression archive format. To access the "long paper" inside, you will need to extract it using specialized software: How to Open the File uum2nKIi.7z
Tools like The Unarchiver or Keka are standard for .7z extraction. Use the official 7-Zip utility (free and open-source)
Apps like ZArchiver (Android) are highly recommended for handling large archives. Why use .7z for a "Long Paper"? uum2nKIi.7z
If the paper is confidential, the .7z format supports strong AES-256 encryption .