Hi, and welcome!
Please see the FAQ: What's a reproducible example (`reprex`) and how do I create one? Using a reprex, complete with representative data will attract quicker and more answers. Just for future reference: this type of error message really not needed.
The key to the error message is
pandoc.exe: test.utf8.md: openBinaryFile: does not exist (No such file or directory)
which, means that either pandoc is not installed at all, or it isn't findable.