Generate book from many articles. How this is possible?

Hello.

I'm new to the list, and searching gave me nothing, so forgive me if this
question was already asked. If this is wrong list to ask such question,
please let me know.

I have many articles in latex. And now I want to create book from them.

The problem is that when I cut and paste text between \begin{document} and
\end{document} latex gives me output with the only one title for the first
article. All other articles, do not have their title.

How can I solve this problem so leave titles for all articles visible?

Thank you for your time,
Peter.