If it's obviously junk from a website (usually spam...), just Google it. If it's something literary, Google the author. If they were still alive in the last 75 years, just put 'Author still alive' or Author only died in xxxx' as appropriate. On Twinkle, it asks for a source or URL if available - just stick it in there. If you do it manually, use {{db-copyvio|Herbert}}  putting the author's info instead of Herbert. I don't know what Page Curation does - I can't stand the thing. If it looks like a copy from a manual, try Google and if nothing comes up, try a copyvio tag explaining that it looks like a manual. It'll be unencyclopaedic anyway, so even if CSD is declined, PROD  should see it off.