Hello Jad!
I did a research of the writable items available on Tibia, and this is what I found:
Yes, all writeable items have a different limit of character length, I leave you a list with the details:
Scroll - Character Length: 511. Once you write you can enter new text.
Valentine's Card - Character Length: 1023. Once written in, it cannot be modified again.
Parchment - Character Length: 1023. Once written in, it cannot be modified again.
Parchment (Yellow) - Character Length: 1023. Once written in, it cannot be modified again.
Document - Character Length: 1023. Once written in, it cannot be modified again.
Book - Character Length: 1023. Once written in, it cannot be modified again.
Book - Character Length: 1023. Once written in, it cannot be modified again.
Book - Character Length: 1023. Once written in, it cannot be modified again.
Labels: Character Length: 79. Labels can be reused and be modified again.
Letter: Character Length: 1999. Can be reused and be modified again.