Keystroke: Ctrl + c
Copy is used to place a duplicate of the current highlighted text into the clipboard, so that you can insert it elsewhere. Use Paste to insert the copy to a new position in the document, or into another application. The text remains highlighted even after you have given a command, (e.g. Ctrl + c to copy), until such time as you use a mouse click - or a navigation key such as one of the arrow keys - to remove the highlighting.
Note: While Perky Duck generally allows you to Copy highlighted braille text, it does not allow it to be Pasted inside the Perky Duck document. Ergo, there is little reason to use Copy except to paste the copied material into an outside application. Beware that the braille font may not be available in that other application, so you may not see braille dots on the screen when you paste.
See also: Edit: Cut