Usage patterns
〈物〉に文字を書くto write characters/letters on something
I wrote letters on the paper.
文字にするto put (something) into writing
It's difficult to put your feelings into words.
文字を読むto read characters/letters
It's hard to read such small letters.
文字が読めないto be unable to read the characters/writing
I can't read the writing on the old letter.
Expressions
黄金の文字gold letters; letters written in gold paint