Using custom OTF fonts in ggplot2

You can try the showtext package, which directly works on OTF fonts.

library(showtext)
font.add("Archer", "Archer.otf")
showtext.auto()
library(ggplot2)
qplot(1:10)+theme(text=element_text(family="Archer"))

Please replace "Archer.otf" by the real filename of your Archer font in the system.

Using showtext does not require embedding the fonts.

You'll need to convert Archer from an OTF to a TTF. From extrafont's github readme:

Presently it allows the use of TrueType fonts with R

I'm amused---I had to do this because my organization also uses Archer. The first hit for this search is purple, so probably that's what I used and it worked just fine.

When having trouble with extrafont it can also be useful to check the available options with fonts(). Then you can verify that your import was successful.

If you save your plot to a PDF, to make sure to embed the fonts as well, using grDevices::embedFonts or extrafont::embed_fonts.