I happened to find that if you want to move all the text in the text box to the body, select the text box (a mesh around the border of the text box, as shown in Figure 1), and then hold down the CTRL key while you right-click the border, and the text in the textbox moves to the body.
As to which paragraph in the text box the text belongs to in the body, it depends on where the mouse clicks. For example, after doing so, the text in Figure 1 will all move to the paragraph with the first paragraph "6" inserted after "6".
To copy all the text in the text box to the body, hold down the Ctrl+shift key and right-click the text box border.
So what if you move or copy only a portion of the text in the box? It's also easy to do this by following these steps:
First, use the mouse to drag and choose Text in the text box, where the border of the text box is slash-like. As shown in Figure 2.
Then, Ctrl-click the border to move the selected text in the text box, press Ctrl+shift to right-click the border to copy the selected text in the text box. The results in Figure 2 Move or copy the selected text to the back of "6".