This is a temporary patch to fix the issues at https://cran.r-project.org/web/checks/check_results_accessr.html, which stem from a call to strsplit() in officedown:::get_fun()
rmd2word() the argument pdf_args may be
used to pass command
line switches to OfficeToPDF when
creating PDF documents. The default setting creates bookmarks in the PDF
file using the headings in the input Word document.ext_img now also works if the file extension of an
input image is capitalised, that is, “PNG”, “JPG” or “JPEG”. In version
1.0.1 it only worked for lower case file extensions.