I'm writing a macro in Excel which finds other files (not Excel files)
with a given name and then opens them. I'm using the Windows registry
to find the programs associated with the files and then using the Shell
command to open the files with the given program. My problem is that
for some programs the Shell command opens a new instance of the program
for each additional file, i.e. each AutoCAD file opens into its own
instance of AutoCAD even if AutoCAD is already running.

So my question is, is there a switch for the Shell command that tells
it to check to see if an instance of a program is already running
before starting a new one, and, if the program is already running,
opens the file with the existing instance? Or is there another way of
doing this without getting into the API of each program in question?

Here's a snippet of my code:

strCmd = appWord.System.PrivateProfileString("", _
"HKEY_CLASSES_ROOT\" & regType & "\shell\Open\command", _
"")

If Len(strCmd) 0 Then
strCmd = Replace(strCmd, "%1", fileWithPath) 'for pdf & dwg files
strCmd = Replace(strCmd, "/dde", "/one " & """" & fileWithPath &
"""") 'for solidworks files
Shell strCmd, vbNormalFocus
Else
MsgBox prompt:="Could not find an application" & vbCr & _
"registered to display file.", _
Buttons:=vbCritical + vbOKOnly, _
Title:="Not Registered"
End If


Thanks!
Eric