Text exports as empty boxes

Outside of the usual "Don't do major editing in Acrobat" warning, this is probably the issue:

The Tahoma text in your PDF has been saved with a different encoding (How old is the file?). This is usually because fonts are (usually) embedded as a subset, sometimes using a custom/different encoding quite different than the Tahoma you have on your system now. (If you look at the Document Properties > Fonts of your original PDF before you edited it, you will see the orginal encoding). When you make your edits in Acrobat, the Tahoma in your system is being used for the changes. Like nost Microsoft TrueType fonts, Tahoma has been greatly expanded from the version from years ago and are now encoded differently. (If you look at your Document Properties > Fonts AFTER your edits, you will see additional listings of Tahoma, with new encodinga)

The end result, is when you copy and paste, you can have text with different encodings in the same "clip"...the "old" encoding doesn't jive with the current encoding and hence garbled text.

Normally, you should be able to export the PDF as a Word file and that will try and sort out the encoding, so I'm curious what file format you exported to.