You can iterate through the Layers and Linetypes collections to find all the layers and linetypes in a drawing.
The following code iterates through the Layers collection to gather the names of all the layers in the drawing. The names are then displayed in a message box.
Sub Ch4_IteratingLayers() Dim layerNames As String Dim entry As AcadLayer layerNames = "" For Each entry In ThisDrawing.Layers layerNames = layerNames + entry.Name + vbCrLf Next MsgBox "The layers in this drawing are: " + vbCrLf + layerNames End Sub