Your step file contains an assembly, which you then try to save as a part.
So it saves a copy and gets rid of the assembly where you have edited the properties.
You need to save the file as a .sldasm document.
The properties you are adding is actually getting added to the imported assembly file. So you need to close the assembly, open the saved part file and add properties to that. Here is a code you can try
Option Explicit Dim swApp As SldWorks.SldWorks Dim swModel As SldWorks.ModelDoc2 Dim bRet As Boolean Dim swImportData As SldWorks.ImportIgesData Dim Err As Long Dim Foldername As String Dim PartNumber As String Dim PartDescription As String Dim SupplierPartNumber As String Dim PartFileName As String Dim nErrors As Long Dim nWarnings As Long Sub Main() Foldername = "C:\PDA" PartNumber = "3231545353" PartDescription = "DARRENS TEST" SupplierPartNumber = "1234567890" Set swApp = Application.SldWorks Set swModel = swApp.LoadFile4("C:\Users\User\Downloads\io1-ac-214.step", "r", swImportData, Err) PartFileName = Foldername + "\" + SupplierPartNumber + ".sldprt" Err = swModel.SaveAs3(PartFileName, 0, 0) swApp.CloseDoc swModel.GetTitle Set swModel = swApp.OpenDoc6(PartFileName, swDocPART, swOpenDocOptions_Silent, "", nErrors, nWarnings) bRet = swModel.AddCustomInfo3("", "Part: Number", 30, PartNumber) bRet = swModel.AddCustomInfo3("", "Part: Description", 30, PartDescription) swModel.Save End Sub
Always use "Option Explicit" as with this you won't miss to define the variables. Also you are using many obsolete/old codes/method, so look in API help files and update them to latest one.
Note that you are using ImportIgesData when you should be using ImportStepData
Also note that SPR1076485 means that this macro won't work in SW2018 or 2019. Bit of a shocker!