@Praveen – as Jarek already said you have to work with the Text Object (which is a super class for formatted text like Character, Paragraph and also the InsertionPoint class amongst others) and use the duplicate() method.
One example: we have two text frames with formatted text on page one of a document.
We want to duplicate the first two characters of one of the text frames after the third character of the other.
Note 1: the end of character 3 of text frame 2 is the fourth insertionPoint counted.
Its index is 3 (counting begins with 0).
Note 2: An empty text frame has no characters but there is one single insertionPoint with index 0.
So it's always good practice to target an insertionPoint.
var myDoc = app.documents; var sourceTextFrame = myDoc.pages.textFrames; var targetTextFrame = myDoc.pages.textFrames; sourceTextFrame.texts.characters.itemByRange(0,1).duplicate ( LocationOptions.AFTER, targetTextFrame.insertionPoints );