Exporting a group of pages as a single or multiple PDF programatically I would appreciate any pointers on this problem.

I have a site which have a set of pages with a given content type, I would like to take all these pages and generate a single (if possible) PDF with the content of each page.

I'm able to write some PHP code but I'm not sure where to start or what modules would help me with this issue. I have checked other answers but they talk more about having an option to click and export a single page where I want to export a dozen/hundreds of pages.

Thanks
I think your best choice here is Views Bulk Operations, you can create a view that lists your content and add the filters and fields you want and then generate the pdf using one of the modules for that matter, such as Views PDF or the Print module. You could generate actions that will be executed by the Bulk operations, one option to do this is to use Rules and Rule sets that are automatically exposed as VBO actions.

You've got a screencast on how to do this in https://www.youtube.com/watch?v=PszjYSq7xQQ and step by step here: http://blog.hsl.virginia.edu/drupalpress/views-pdf-vbo-rule-sets-thousands-of-custom-forms/