Hi, and welcome!
Quick overview of the chain to create PDF:
rmarkdown -> pandoc -> MIKTEX -> pdf
The rmarkdown takes care of installing pandoc, but it's up to the user to install MIKTEX (in WinWorld) where it's expected.
The POLR (path of least resistance) here is to move pdflatex.exe to C:/Users/jsnyd/AppData/Local/Programs/MIKTEX~1.9/miktex/bin/x64, along with any other files in its current directory. (I'd be more precise, but I haven't been troubled with Windows since XP.)