Make a project using below code. Compile it and call it SendKeysA.exe

Code:
Dim ReturnValue As Long

Private Sub Cpmmand1_Click()
 ReturnValue = Shell(App.Path & "\SendKeysB.exe", 1)
End Sub

Private Sub Command2_Click()
 AppActivate ReturnValue
  
 SendKeys "Hello from program A" & vbCrLf
 Exit Sub
 
 MsgBox "Press OK to do a Ctrl+M - " & Chr(34) & "^M" & Chr(34)
 SendKeys "^M", True      ' Send Ctrl + M
  
 MsgBox "Press OK to do a Ctrl+M - " & Chr(34) & "^(M)" & Chr(34)
 SendKeys "^(M)", True    ' Send Ctrl + M
 
 MsgBox "Press OK to do a Alt+S - " & Chr(34) & "%S" & Chr(34)
 SendKeys "%S", True      ' Send Alt + S
 
 MsgBox "Press OK to do a Alt+S - " & Chr(34) & "%(S)" & Chr(34)
 SendKeys "%(S)", True    ' Send Alt + S
End Sub
Now make another project and put a Text1 on it. Compile it and call it SendKeysB.exe

Run SendKeysA.exe only. Click on Command1. SendKeysB.exe will be launched. Now click on Command2.