Convert a file to binary for insertion in an xml file (to work as an attachment)

I've seen things on the web that seem close to what I'm looking for, but I haven't quite made it work.

If I look inside of an MS Infopath XML file, the atttachments appear to be binary code stored between tags. This should be easy to create with VBA, but I don't quite have the background to do it.

The code I'm using is below. In this case I'm trying to get the text from an Excel file that I can embed. When run, the error should be something about the arguments being of the wrong type.

Code:

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Const adTypeBinary = 1Const adTypeText = 2
Const adModeReadWrite = 3


Sub RunThis()
    bin2var "c:\users\n902797\documents\IYYMMCC Validation.xlsx"
End Sub


Function bin2var(filename As String) As String
    Dim f As Integer
    f = FreeFile()
    Open filename For Binary Access Read Lock Write As #f
        bin2var = Space(FileLen(filename))
        Get #f, , bin2var
        thestring = BytesToString(bin2var, CdoUS_ASCII)
    Close #f
End Function


Function BytesToString(bytes, charset)
    With CreateObject("ADODB.Stream")
        .Mode = adModeReadWrite
        .Type = adTypeBinary
        .Open
        .Write bytes
        .Position = 0
        .Type = adTypeText
        .charset = charset
        BytesToString = .ReadText
    End With
End Function

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