Do these need to be pdfs? Some are already available online, you can print to pdf or something if you need the format. Lots of these were originally published in newspaper articles or pamphlets so you wont get book style pdf formatting :

https://monthlyreview.org/2009/05/01/why-socialism/

https://theanarchistlibrary.org/library/petr-kropotkin-the-conquest-of-bread

https://www.marxists.org/archive/marx/works/1848/communist-manifesto/index.htm

www.marxists.org has a lot of texts available also. Sorry too lazy for link shortening.