To mix any audio data from either the Windows or the internal clipboard with the current wave open Edit/Mix Paste menu. In the window that will show up set the necessary Amplify Select and Amplify Paste values, select the file from which you are going to paste audio data.
Clipboard data is overlapped starting at the current insertion point or selection. If the format of the waveform data on the clipboard differs from the format of the file it is being pasted into, AVSAudioEditor converts it before pasting.