SldWorks swApp = new SldWorks();

ModelDoc2 swModel = default(ModelDoc2);
 ModelDocExtension swModExt = default(ModelDocExtension);
 DrawingDoc swDrawDoc = default(DrawingDoc);
 Sheet swSheet = default(Sheet);

 var docSepc = (DocumentSpecification)swApp.GetOpenDocSpec(input);

 swModel = swApp.OpenDoc7(docSepc);
 swModExt = (ModelDocExtension)swModel.Extension;

 ExportPdfData swExportPDFData = default(ExportPdfData);

swExportPDFData = (ExportPdfData)swApp.GetExportFileData((int)swExportDataFileType_e.swExportPdfData);

boolstatus = swExportPDFData.SetSheets((int)swExportDataSheetsToExport_e.swExportData_ExportSpecifiedSheets, (arrObjIn));
 swExportPDFData.ViewPdfAfterSaving = false;
 boolstatus = swModExt.SaveAs(filename, (int)swSaveAsVersion_e.swSaveAsCurrentVersion, (int)swSaveAsOptions_e.swSaveAsOptions_Silent, swExportPDFData, ref errors, ref warnings);
 swApp.CloseAllDocuments(true);
 swApp.ExitApp();

swApp = null;

--------------------------------------------------------------

​​​​​​​Here is snapshot of postman