A file extension is a suffix that is added to the end of a file name after a dot. It is usually two to four letters long. File extensions help Windows and other operating systems to know the standard ...

When you copy a file or folder to the same location on your local drive in Windows PC, a copy of that file or folder will be created with the – Copy extension added at the end of the file/folder name ...

Microsoft hides file extensions in Windows by default even though it's a security risk that is commonly abused by phishing emails and malware distributors to trick people into opening malicious files.