A .7z file is a compressed archive file created by the 7-Zip compression tool. It is similar to other compressed formats like ZIP and RAR, but uses a higher compression ratio and supports AES-256 encryption. The 7z format is newer than the ZIP file format and provides a high level of compression. One benefit of using the 7z format is that it can be used with files that you want to split into several smaller parts, which is especially helpful when transferring or downloading larger files or folders.

To open a .7z file on Windows, you can use third-party apps like 7-Zip or Unzip One. Unzip One is a free and safe alternative to WinRAR, WinZip, and BreeZip. To open a .7z file using Unzip One, you need to download and install the software, then follow these simple steps:

1. Right-click on the .7z file you want to extract.
2. Select "Unzip One" from the context menu.
3. Choose the location where you want to extract the files.
4. Click "Extract".
5. The extracted files/folder will be saved to the location you chose. Click "Show extracted files in folder" to view them.

It is important to note that 7z files are no less safe than any other similar file formats. However, as with any file, you should only open 7z files from trusted sources because there is always the possibility that a 7z file could be malicious.