LittleBobbyTables explained in his comment why your first example is not working.
As for your second example, this does not work because you do not insert spaces between the end of winword.exe and the file path, so your command line looks like this:
"C:\Program Files\Microsoft Office\Office\winword.exe""C:\UserGuide.doc"
, winword.exe, , , 64- Windows, MS Office. Word:
Set oWord = CreateObject("Word.Application")
oWord.Visible = True
oWord.Documents.Open "C:\UserGuide.doc"