Preview erases the capability to recognize text after I annotate a pdf file.

It seems if I edit a pdf preview document that has recognizable text (you CAN use CMD+F and copy and paste the text), it the document LOSES it ability to recognize the text. If I copy some highlited text, it will paste as some kind of code. When I say edit a document, I mean take a note, highlite, ect. It also loses this ability if I change the file name.



I am a student and would like the ability to edit my textbooks and retain their ability to Command + Find. I really like preview and do not want to use another program, if possible.



I had the same problem in Snow Leopard, I read a post somewhere that it had been resolved in Lion, which is why I upgraded to Mountain Lion (figured it would still be resolved).



Any advice would be greatly appreciated.