When doing a Find & Replace you can limit the scope of the search to a specific area. This is done by adding a temporary crop to the relevant pages then removing it after the search has completed.

  1. Crop the relevant pages using the crop tool. 
    This will not delete anything from the PDF but simply hides text and graphics outside the cropped area.
  2. Choose File->Preferences... and in the Editing tab, ensure Include cropped text when editing is off.
  3. Do the Find & Replace as normal.
    By default Infix Pro PDF Editor will not bother searching for text outside the crop. However, there is a preference option which can change this behaviour. 
  4. Remove the crop by choosing Pages->Remove Crop...