Export to Word based on Word template

There are plenty of stable PHP libraries, free and paid, just google for them.
Few examples: https://github.com/PHPOffice/PHPWord or https://www.tinybutstrong.com/opentbs.php

However, very often you do not ned any fancy MS Word features. If all you need is to put some text with basic formatting that can be later opened in MS Word, you can do int into much simpler Rich Text Format (https://en.wikipedia.org/wiki/Rich_Text_Format). There is also a number of libraries with good enough support for RTF.