I'm running RStudio (0.98.1091) and Texworks MiKTeX (2.9 64 bit) on Windows 7.
My PATH environment variable is set and includes the complete path to the MiKTeX directory where pdflatex lives:
"F:\Tools\MiKTeX 2.9\miktex\bin\x64". If I open a command shell I can see the PATH is set; I can also invoke pdflatex simply by typing in the command shell.
I can see my PATH variable with the correct path to the MiKTeX /bin folder if I open RStudio and type
Sys.getenv("PATH") in the console.
However, when I run Rmarkdown in Rstudio it complains that there's no pdflatex available.
No TeX installation detected (TeX is required to create PDF output). You should install a recommended TeX distribution for your platform: Windows: MiKTeX (Complete) - http://miktex.org/2.9/setup (NOTE: Be sure to download the Complete rather than Basic installation)
Google searches bring back several questions like mine, except for MacOS, like this:
Is there any way for me to tell RStudio where MiKTeX is installed so I can generate PDFs?