[R] problem opening pdf device on Windows 7

[anupam]

I can not open PDf device. Acrobat is closed. I have checked archives but 
could not find a solution. What should I do?

> cont.cdfplot("myanalysis.pdf", myanalysis$CDF, ylbl.r="Stream Length (km)")
Error in pdf(file = pdffile, width = width, height = height) : 
  unable to start device pdf
In addition: Warning message:
In pdf(file = pdffile, width = width, height = height) :
  cannot open 'pdf' file argument 'myanalysis.pdf'

Then I tried:

> pdf()
Error in pdf() : unable to start device pdf
In addition: Warning message:
In pdf() : cannot open 'pdf' file argument 'Rplots.pdf'