I couldn't find a macro to do this so I made one. Set your paths (see comments).

Dim swApp As SldWorks.SldWorks
Dim Part As ModelDoc2
Dim result As Long
Sub main()
    Dim Path As String
    ' SET YOUR STL OUTPUT PATH
    Path = "C:\Stuff\Files\3D printing\STL\"
    
    Set swApp = Application.SldWorks
    
    Set Part = swApp.ActiveDoc
    If Part Is Nothing Then Exit Sub
    If Part.GetType = swDocDRAWING Then
        Exit Sub
    End If
    
    Dim Extension As String
    Dim PartName As String
    PartName = Part.GetTitle
    
    If InStr(PartName, ".SLDPRT") = 0 Then
        MsgBox "Save part first"
        Exit Sub
    End If
    
    Call SelectAll(Part)
    
    Extension = Mid(PartName, InStrRev(PartName, "."))
    PartName = Replace(PartName, Extension, ".stl")
    Path = Path & PartName
    result = Part.SaveAs3(Path, 0, 0)
    Call open_s3d(Chr(&H22) & Path & Chr(&H22))
End Sub
Sub open_s3d(stlPath As String)
    Dim sFullPathToExecutable As String
    sFullPathToExecutable = "C:\Program Files\Simplify3D\Simplify3D.exe" & Chr(&H20) & stlPath
    Shell sFullPathToExecutable
End Sub
Sub SelectAll(swModel As SldWorks.ModelDoc2)
    ' Select all edges in the part,
    swModel.Extension.SelectAll
End Sub

Message was edited by: Jason F.