Javascript Error code 55: does not support

i'm trying to run the following script:

Eu estou tentando redoar o seguinte script

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var myDocument = app.documents.add();

var myTextFrame = myDocument.pages.item(0).textFrames.add();

myTextFrame.geometricBounds = ["6p", "6p", "24p", "24p"];

myTextFrame.contents = "Hello Worlfgfgd!";

//Improved Hello World!

//Enter the name of a font on your system, if necessary.

try{

    myFont = app.fonts.item("Arial");

}

catch (myError){};

var myDocument = app.documents.item(0);

with(myDocument){

    var myPage = pages.item(0);

    var myBounds = myGetBounds(myPage,myDocument);

    with(myDocument.pages.item(0)){

//Get a reference to the text frame.

        var myTextFrame = textFrames.item(0);

//Change the size of the text frame.

        myTextFrame.geometricBounds = myBounds;

        var myParagraph = myTextFrame.paragraphs.item(0);

        myParagraph.appliedFont = myFont;

        myParagraph.justification = Justification.centerAlign;

        myParagraph.pointSize = 48;

    }

}

//myGetBounds is a function that returns the bounds

//of the "live area" of a page.

function myGetBounds(myDocument, myPage){

    var myPageWidth = myDocument.documentPreferences.pageWidth;

    var myPageHeight = myDocument.documentPreferences.pageHeight;

    if(myPage.side == PageSideOptions.leftHand){

        var myX2 = myPage.marginPreferences.left;

        var myX1 = myPage.marginPreferences.right;

    }

    else{

        var myX1 = myPage.marginPreferences.left;

        var myX2 = myPage.marginPreferences.right;

    }

    var myY1 = myPage.marginPreferences.top;

    var myX2 = myPageWidth - myX2;

    var myY2 = myPageHeight - myPage.marginPreferences.bottom;

    return [myY1, myX1, myY2, myX2];

}

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but it's always givve me this message error:

Javascript error!

Error code 55

error string: Object does not support the property or method 'documentPreferences'

Mechanism main

File:C:\Users\ ...........Scripts\Scripts Panel\Teste.jsx\Source.jsx

Line 30   

Origin:       var myPageWidth = myDocument.documentPreferences.pageWidth;

This javascript script was copy and paste exactly as it is. i founded this in ADOBE INDESIGN CS6 SCRIPTING TUTORIAL ¬¬

eu achei esse codigo num pdf da adobe: Adobe Indesign Scripting Tutorial e ele sempre me dá o erro supracitado. Alguém?