Looks like the articles in the document repository consist of separate pages (png files) per article.
If there's no pdf/djvu versions of the articles (can you confirm @Ambrosiani ?), they will have to be created as part of the upload.
Preferably Djvu as that's heavily used by wikisource: https://commons.wikimedia.org/wiki/Help:DjVu
https://commons.wikimedia.org/wiki/Help:Creating_a_DjVu_file
See also https://en.wikisource.org/wiki/User:GrafZahl/How_to_digitalise_works_for_Wikisource