WARNING 'qpdf' is needed for checks on size reduction of PDFs
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I am trying to check a package that I have built (with vignette) using `R CMD check --as-cran [my package]` in my windows command prompt. All goes well until I get the message,
 
    WARNING 'qpdf' is needed for checks on size reduction of PDFs

I have downloaded qpdf, put the unzipped folder in my program files directory, and added the bin folder to the PATH. 

Not quite sure what else I need to do? I have the feeling I have not installed qpdf correctly or I need to build this program itself? I have read through the readme files in qpdf and manual which appear to be more aimed at unix users (which I have no experience with... I am your standard/regular windows user with little to no programming experience outside of statistical languages). I have had a go at trying to build qpdf using cgywin, but ended up failing to install zlib and prec. Any tips? 