Backlinks in PDF file ?

I've read this on reddit a while ago but couldn't find that comment again so I'm asking here if anyone knows about this and if it works

I think it was a post about building backlinks with forums or something, guy who commented said that those are no follow and are of no value but if u added backlink into pdf file it would work. Anyone done this before ?

Adding backlinks into a PDF file has no effect whatsoever. Backlinks are like a link that goes from another site to your website and it gives a bit of that website's "juice" to you meaning your website ranks higher than before without the backlink. You generally want related back links so let's say you are a doctor and you have a nutrition website. Health related websites, even body building or gym websites that give backlinks to you make you rank higher than websites who offer law services for example.