A file extension is the suffix at the end of a filename (like .docx, .jpg, .exe) that tells your operating system which program should open it. Changing the extension simply renames the file; it doesn't directly damage your computer hardware. However, it fundamentally misrepresents the file's actual contents. This forces your system to try opening the file with the wrong application. Your computer won't catch fire, but this action often leads to errors, crashing applications, or files becoming unusable because the underlying data format remains unchanged.

For example, renaming a photo file from .jpg to .docx won't magically make Microsoft Word understand the image data – Word will likely fail to open it or display garbage. A more serious risk involves misidentifying potentially harmful files. Renaming a malicious .exe program to something like .txt might bypass basic security warnings, tricking you into thinking it's just a harmless text file. If you then try to open it expecting text, you could unknowingly execute the malware.

While merely renaming an extension won't physically harm the computer itself, the consequences can be severe: unexpected software behavior, lost productivity fixing the issue, corrupted files if you incorrectly "save" after the wrong app fails to open it, and significant security vulnerabilities if malicious files are disguised. The best practice is to convert files properly using dedicated tools or software features designed for format changes, not by manually altering the extension. Always be extremely cautious about opening files from untrusted sources, regardless of their extension.