Unknown Unicode �

[makinero]

Unicode HEX: U+FFFD
ASCII value: 65533
UTF-8 (hex) 0xEF 0xBF 0xBD (efbfbd)
UTF-16 (hex) 0xFFFD (fffd)
UTF-16 (decimal) 65 533
UTF-32 (hex) 0x0000FFFD (fffd)
UTF-32 (decimal) 65 533
�

I have a file names in the texts, which means this character and how to transform it into a valid character.

[HolgerK]

I have a file names in the texts, which means this character and how to transform it into a valid character.

You can't recover the original character without the original source:
https://en.wikipedia.org/wiki/Specials_(Unicode_block)#Replacement_character