The Windows sound recorder is a great tool for recording gretings in the correct format.
Converting format, Editing, Merging, Splicing is a completely different matter.
As this is a case of converting format, the main issue is loss of quality. One option might be to play the sound with one player and record via another.
I haven't tried this with wavepad, but I wouldn't be surprised if it is capable.
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Occam's Razor - All things being equal, the simplest solution is the right one.