Different ways of displaying documents between Adobe Reader and Preview

I use an e-book reader (Icarus Excel) to make notes on PDF files. When looking at the output PDF (which merges the notes with the PDF document) in Adobe Reader, the notes are present. However, the same document, when opened in Preview, does not display the notes. What would be the reason behind different ways of displaying the same document in the two programs and how to make Preview "see" the notes?