Provided a file of unknown type, we are interested in its filename and extension.
1. We copy the filename
2. Use an online Caesar's Cipher tool at [decode](https://www.dcode.fr/caesar-cipher)
3. Paste the encrypted filename and Try all the possible combination button.

The result is shown on the left side, that the encrypted text is decoded at shitf +3
we get the flag contents, now we combine it and with the flag format as *flag{....}*, and submit the flag.