title: How to build qpdf on Windows?
body: <p>When running the checks for my R-package (via <code>devtools::check()</code>) I face the warning <code>''qpdf' is needed for checks on size reduction of PDFs</code>. I found <a href="https://stackoverflow.com/questions/11738844/qpdf-exe-for-compactpdf">this question</a> were it was suggested (if I understood the answer correctly) to run <code>Sys.which(Sys.getenv("R_QPDF", "qpdf"))</code> and see whether qpdf is found or not. In my case this just returns</p>
  
  <p><code>qpdf
    ""</code></p>
  
  <p>so, I think I didn't install qpdf correctly. Unfortunately <a href="https://github.com/qpdf/qpdf/blob/master/README-windows.txt" rel="noreferrer">it seems to be quite complicated to install qpdf on Windows.</a> My first side question is: does it really is so painful and complicated to install qpdf for Windows or is there an easy solution?</p>
  
  <p>I've followed the instructions until it is said to add C:\MinGW-w64\bin and C:\MinGW-w64\lib\mingw to the PATH variable. But then I don't find further specific instructions to <em>install</em> qpdf, only about how to <em>build</em> qpdf with different other programs. The second side question is: is my assumption correct that after I've <em>build</em> qpdf it is <em>installed</em>? But the real question is: <strong>What is the best way to build qpdf?</strong> I tried the <code>./config-mingw32</code> and <code>./config-mingw64</code> commands from the section "Building with MinGW" in my C:\MinGW\msys\1.0\bin\bash.exe but got the error messages <code>./config-mingw32: No such file or directory</code> and have no idea how to fix this issue.</p>
  
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  <p>I'm using Windows 10, R version 3.3.2 Patched (2017-01-07 r71934) -- "Sincere Pumpkin Patch" and RStudio 1.0.136.</p>