One reason an RTF file produced by Word would be larger than one produced by WordPad is that the Word RTF will contain a lot of data regarding Styles, etc., which WordPad doesn't support.
You could indeed automate WordPad, using code like:
Sub Demo()
Dim StrWdPd As String, StrFlNm As String
StrWdPd = Environ("ProgramFiles") & "\Windows NT\Accessories\WordPad.exe"
StrFlNm = "C:\Users\" & Environ("Username") & "\Documents\Test.rtf"
Shell StrWdPd & " " & Chr(34) & StrFlNm & Chr(34), vbNormalFocus
SendKeys "^s%fx"
End Sub
Cheers
Paul Edstein
[MS MVP - Word]