Thanks Idolse. However, despite following these posts' instructions Calibre isn't detecting or removing the offending text from the document.
I copied and pasted the text from the original PDF into the field after clicking on the "wizard wand". Then I clicked on "test". It's supposed to then highlight it. In one case it shows 1 occurance, other times, zero occurances. I convert the book anyway, then preview the new copy. The text is still there.
Obviously I'm either doing something wrong or Calibre is. I don't know which.
And here is the text that I want to delete:
"Generated by ABC Amber LIT Converter, http://www.processtext.com/abclit.html"