inst/doc subdirectory
  of R source packages archives (.tar.gz) found in a local
  package repository.  All pdf files found in inst/doc will be extracted.
  With extractHTMLDocuments, all HTML files except
  index.html will be extracted.
    Only source
  package archives will be processed.  The extracted pdf 
  or HTML files will be
  extracted under destDir and will be found in
  PKGNAME/inst/doc/.
  Prior to extraction, all pdf files in destDir/PKGNAME/inst/doc
  will be removed.
extractVignettes(reposRoot, srcContrib, destDir)
extractHTMLDocuments(reposRoot, srcContrib, destDir)reposRoot to the source packages.  In a standard CRAN-style
    repository, this will be src/contrib./vignettes .