How to write to a text file all the contents of another text file from a specific location?

Question

Delphi

There is a text file 1.txt. And another text file 2.txt.
File contents 1.txt.

Строка 1
Строка 2
<Тут нужно вставить содержимое текстового файла 2.txt>
Ещё строка

How can I insert the contents of the text file 2.txt into this location of the file 1.txt?
The contents of the text file 2.txt are lines. And very long - can be more than 500 characters.