Character Codes

Encoding is the process of transforming a set of Unicode characters into a sequence of bytes.
Decoding is the process of transforming a sequence of encoded bytes into a set of Unicode characters.

Encoding

Remove all the non UTF8 characters from a string.
You can use encoding which is the process of transforming a set of Unicode characters into a sequence of bytes.

string textAfter = System.Text.Encoding.UTF8.GetString(textBefore);

GetBytes

This encodes a set of characters into a sequence of bytes.

byte[] bytes = System.Text.Encoding.Default.GetBytes(textBefore);