I speak spanish, sorry for my bad english (im using google translate).
I want to export data from preguntas y respuestas (possible spam link removed) using PHP to a document compatible with LO
The basic way of doing this is, as you mention, reusing or creating a PHP script that exports data (presumingly from the database that the given site runs on) to a file or a set of files that can be opened with LibreOffice. LibreOffice can handle many kinds of file formats — which is the best for you depends on your goal.
You could create a table-like document in CSV (Comma separated values) or TSV (Tab separated values) format and import them in Calc. Or you could save each page as HTML or some XML-based file format like DocBook and open them in Writer. If you have access to the database that is behind the website (for example MySQL or PostgreSQL) from the computer you are using LibreOffice on, you could even use Base to connect to the database and create labels.
Examples of how to use PHP to create documents of any of the above types is, in my opinion, beyond the scope of this Q&A website. You could try to find answers to specific questions about programming with PHP on StackOverflow.