Welcome to the community
So each line can be of any length or are there specific number of characters that are considered as a line?
If each line has specific characters then use substring with the number of characters
Str.Substring(0,“Number of characters for 25 lines”)
else use str.SPlit(Environment.Newline,0,25)
This will split the string with 25th occurrence of new line character
cheers
cheers