Is an Unknown File Safe?
No extension proves safety
A file extension is not a safety certificate. Attackers can use common extensions such as PDF or DOCX to hide malicious behavior, and they can rename executable files to look like documents.
Safety depends on the source, the actual file content, the software used to open it, and whether the environment is protected.
Check executable and script risks first
Files that run code directly, such as EXE, DLL, BAT, CMD, MSI, and SYS, deserve extra scrutiny. The same applies to container formats that can hold executable content, including ZIP, 7Z, and RAR.
If a file is executable and you did not expect it, do not open or install it. Verify the download URL, publisher, and checksum through a channel you trust.
Look for the source and intent
Ask whether the sender expected you to receive this file. Check the actual email address, not only the display name, and watch for urgent language that pushes you to open an attachment immediately.
If the request seems unusual, contact the person or organization through their official website or a known phone number instead of clicking links in the message.
Keep software updated and open cautiously
Updated operating systems, browsers, and viewers reduce the risk of known format vulnerabilities. You can open a suspicious document in a viewer with macros disabled or in an isolated environment such as a virtual machine.
Do not enable macros, add-ins, or scripts inside a file unless you are confident the file is legitimate and you need that functionality.