While editing text, you can use the “Cut”, “Copy”, “Paste” toolbar buttons 
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To copy a text fragment, select it (click the left mouse button at the beginning of the text; then, while holding the Shift key, click at the end of the text you want to select), and click the “Copy” button 
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To paste the text, click the left mouse button at the location you want to insert the text, and click the “Paste” button 
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You can also use the standard key combinations (Ctrl + C to copy, Ctrl + V to paste, Ctrl + X to cut) or click the text box using the right mouse button, and use the pop-up menu.