Thank you Ariel, but I am receiving this message:

Object does not support the property or method 'characters'

Sami

Thank's again Ariel,

I am a beginner in Java Script and I don't know what I am doing wrong.

Please take a look:

main();

function main(){

          mySetup();

          mySnippet();

          myTeardown();

}

function mySetup(){

}

function mySnippet(){

          if (app.documents.length != 0){

                    if (app.selection.length == 1){

                              switch (app.selection[0].constructor.name){

                                        case "InsertionPoint":

                                        case "Character":

                                        case "Word":

                                        case "TextStyleRange":

                                        case "Line":

                                        case "Paragraph":

                                        case "TextColumn":

                                        case "Text":

                                        case "Story":

                                                  myProcessText(app.selection[0]);

                                        break;

                                        case "TextFrame":

                                                  myProcessText(app.selection[0].texts.item(0) );

                                                  break;

                                        default:

                                                  alert("The selected object is not a text object. Select some text and try again.");

                                                  break;

                              }

                    }

                    else{

                              alert("Please select some text and try again.");

                    }

          }

}

function myTeardown(){

}

function myProcessText(myTextObject){

}

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

var myPage = myDocument.pages.item(0);

var myTextFrame = myPage.textFrames.item(0);

var myTextObject = myTextFrame.parentStory.characters.item(0);

var myStory = myDocument.stories.item(0);

var myStringArray = myTextFrame.lines.everyItem().contents;

myPara = app.selection[0];

myLines = myPara.lines;

for (var i =0; i<myLines.length; i++){

    myFinds = myLines[i].findText(ת);

myFinds[-1].contents = "z";

}

Sami

Thank you very much Jump_Over!

It works!

Now I am doing the final adjustments.

Sami