Please use the PasteHTML() API.
PasteHTML()
This method is used for pasting the specified HTML into a range within an editor document. If anything is selected, the selection is replaced with the new HTML and text.
Example:
// get the cute editor instance
var editor1 = obj_Editor1;
// pasting the specified HTML into a range within a editor document
editor1.PasteHTML("Hello World");
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