You can copy text from jPreTeX to another editor by the following way :
    you select the text you want in jPreTeX, then you hit the Copy button to put it in the clipboard. Then you click in the other editor at the location you want it and by hitting Ctrl + v keys or the paste button you paste it in the document in the other editor.

        You can copy text from another editor to jPreTeX by the following way :
    you select the text you want in the other editor, then you hit the Ctrl+c keys (or the right editor command for copying) to put it in the clipboard. Then you click in the jPreTeX screen at the location you want it and by hitting  the paste button you paste it in your document.