Àííîòàöèè - are PDF document objects such as note, sound, movie and etc. placed on the document page. 

Many standard types of the annotations may be on the page in opened or closed condition. When annotations are closed they are displayed on the page in conditional form depending on their type, for example icon, mailbox or stamp. When user activates annotation clicking the mouse on annotation will show object connected with it, for example window with text note or video clip or sound playing.