File-type masquerading is the practice of making a malicious file look like a harmless one. Attackers may use misleading names, double extensions, altered icons, or packaging tricks so that a document appears to be a PDF, a font, an image, or another trusted format. The goal is to lower suspicion long enough for a user to open it.
This technique matters because many attacks begin with trust, not code. If a file looks routine, a recipient is more likely to click it, and a security tool may treat it as lower risk unless it inspects the real content. In phishing, masquerading is often paired with business-themed lures and attachment delivery. Defenders counter it by showing full file extensions, checking MIME type and magic bytes, filtering risky attachments, disabling unnecessary file handlers, and training users to question unexpected files that claim to be common Windows or office formats.