Some PDF files you have may contain superscript text like this:

By default, PDF2XL will convert the superscript into your output, but be advised that it will not retain the formatting of the superscript, so the text will not be smaller or aligned at the top. 

If you prefer not to have the superscript converted, which is often the case if you don't wish to keep footnotes, go to Options > Format and remove the check from the box labeled "Convert superscript".

If your preview doesn't change, try clicking the Preview sizes, colors option on the Preview Pane toolbar.

After you convert your file, you should not see the superscript text in your output.