How to erase files permanently from Windows computer?

1. Built-in Windows command-line utility that overwrites free space on a drive, making previously deleted files unrecoverable.

How to erase files permanently: 
- Open Command Prompt as Administrator.
- Run: cipher /w:C:\ (replace C:\ with the drive letter you want to wipe free space on).

Limitations: It doesn't erase files permanently; instead, it overwrites free space, ensuring deleted files can't be recovered from that space.
Best use: To clean up residual recoverable data after deleting sensitive files.

2. Secure Formatting, Performing a low-level or secure format that overwrites the entire drive.
Note: Standard format in Windows (via Explorer) does not securely erase data. You need specialized tools or bootable media that supports secure formatting.
Advanced approach: Use third-party tools like DBAN (Darik's Boot and Nuke) or manufacturer-provided disk wiping utilities to wipe entire drives.

Summary

• For permanent deletion of specific files, use a reputable file shredder (Eraser, BleachBit).
• For preventing recovery of previously deleted files, run cipher /w on free space.
• For erasing files permanently before sale, use dedicated disk wiping tools (DBAN, manufacturer utilities).
• No single built-in Windows feature offers comprehensive secure file deletion for individual files, so third-party tools are your best bet for sensitive data.