In somewhat of an oblique comment to Joemikeb's post, the variable I'd like to bring up here is the role of the
source of the PDF, how (by what software) it was generated and possibly altered. Although it doesn't appear to have any direct bearing on the Preview text box issue you're dealing with, there is a known issue with marking up (certain) PDFs in Preview. It appears to be due to a bug, which causes Preview not to follow proper convention when marking up PDFs, effectively corrupting them. Some of the details are discussed in a reader report starting
here.
