COLLECTED BY
Collection: MSAG-PDF-CRAWL-2017
Microsoft Academic Graph public corpus (Feb 2016) PDF URLs, filtered to remove large sites (pubmed, citeseerx, arxiv) and already-crawled URLs.
TIMESTAMPS
The Wayback Machine - https://web.archive.org/web/20170810020623/http://repositorio.chporto.pt/bitstream/10400.16/493/1/pdf.4.pdf