Selecting text, copying and then pasting is not the smart way of copy-pasting. If you have used PuTTY any time, you may have noticed that the action of selecting text, copies the selected text into the clipboard. All you need to do is a right click to paste it back in PuTTY.
Similar functionality exists in SAP GUI, which may not be activated by default. You can activate it by selecting the following option:
Select "Quick Cut and Paste" option from GUI to enable the option.