Hi Scratch_MM,
Yes optimising for pdf´s still matters and follow some specific optimization rules, You can find a great post about this on SEJ https://www.searchenginejournal.com/pdf-seo-best-practices/59975/.
In relation to competing with the parent page, the pdf is just another page and as such eligble for ranking dependent on the content. If the pdf contains the same content as the parent page than it would be better to use a canonical to the parent page. Otherwise its will compete as much as normal pages would do, based on there content.
Hope this helps