Outputting to PDF is not currently supported because it is not a knitr feature (it's usually done using rmarkdown::render().

However, it seems like many people associate PDF output to knitr because of the "knit" button in RStudio, and many people have wondered why you can't ezknit into PDF.

@ttimbers asked about this in the package review, @klmr mentioned this in issue #8 , and @PedramNavid recently mentioned this in a high profile Twitter convo

Perhaps it's time to look into somehow supporting PDF as an output. I'm not sure what the best way would be: should we just add an extra parameter that lets you specify you want PDF output, and if that's set then the flow would be: input Rmd --> ezknit to md --> render to pdf ?