Question: 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:

<https://support.rstudio.com/hc/communities/public/questions/203561546-RStudio-can-t-detect-pdflatex-No-Tex-installation-detected->

Is there any way for me to tell RStudio where MiKTeX is installed so I can generate PDFs?

Answer: 
Ulrike Fischer's comment is correct. In RStudio for Windows, I can do this:

```
Sys.setenv(PATH = paste(Sys.getenv("PATH"), "C:\\RMathew\\PortableApps\\MikTeX\\miktex\\bin", sep=.Platform$path.sep))

```

which will let me use pdfLaTeX for that session. If you want RStudio to remember this command each time you start RStudio, you have to add the command to your `.Rprofile` file.

Note the use of the double backslash for each folder.
If it still fails once you've set the environment PATH, I found that restarting the PC does the trick.