Paste the content of the program’s clipboard (prepared by COPY or CUT commands) into the active waveform starting at the selected pulse. The waveform will be extended if needed (zero-amplitude pulses will be appended to all waveforms):

You can override existing amplitude and/or timing information according to settings in “Preferences” dialog. Click on a corresponding check-box. You can make your choices permanent by checking “Remember and do not ask again”. You can then access this dialog again using PASTE PREFERENCES… item described below.