I send this to DOS from Access:
Dim strCommand As String
Dim strVariableFrom, strVariableTo As Variant
strVariableFrom = "test.tif"
strVariableTo = "test.PDF"
strCommand = "c:\imagemagick\imagemagick\convert.exe" & " " & strVariableFrom & " " & strVariableTo
Shell ("Cmd /k" & strCommand)
When it gets to the DOS prompt it looks like this and fails:
convert.exe 'test.tif' 'test.pdf'
Note the single quotes.