Thanks, I used the Unicode Hex Input on a Mac and copied the text file to Pleco iOS and Pleco Android, which unfortunately didn't show me the characters I was looking for, one empty one and another random one.
I downloaded a Unicode input app on Android, and the fact that it used the clipboard as a means of getting special Unicode characters into other apps indicates to me that Android's clipboard should work fine for any special Unicode character. If you had the characters inside Pleco and they were garbled after copying, this suggests to me that ARChon's Copy-and-Paste integration, if it exists, somehow corrupts the clipboard for special characters.