Save SaveAs this.saveAs

Hi
I tried on the file the formulas listed on this page https://www.pdfscripting.com/public/How-to-Save-a-PDF-2.cfm with Acrobat DC. The formula var oMyDoc = <… PDF being operated on…> 
app.execMenuItem ("Save", oMyDoc); works.
Other functions do not work, app.execMenuItem ("Save"); and -this.saveAs ("/ c / temp / temp.pdf");
etc
Please, can anyone explain to me why the functions indicated in the tutorial do not work?