knitr包只能够将R markdown文件转为html格式,若想要将其转化为pdf格式,还要安装另一个包
# Install and load package
install.packages("rmarkdown")
library("rmarkdown")
# Convert
render("../Your_MD_File.md", output_format="pdf_document")
Reference
http://*.com/questions/11025123/how-to-convert-r-markdown-to-pdf