Work through this in order
- Keep a copy of the original and inspect the filename extension
- Use the signature detector to identify the actual container format
- If the format is unknown inspect the first bytes in the hex viewer
- Search for a trustworthy native viewer only after identifying the format
- Avoid uploading confidential files to random online converters
Use the matching tool
Inspect a local copy with Unknown File Extension Opener. After the check, save or repair files only using trusted software that supports the format.