In PDF, an annotation is an item separate from the page content which is located in a layer above the page content. For example, like a Post-It® note is located over the text of a page.
Annotations can take many forms. The following is a list of the most common annotations used in PDF:
- Free Text
- Rubber Stamp
- File Attachment
PDF form fields and digital signature fields are types of “Widget” annotations.
Information on annotations can be found in Section 12 – Interactive Features of ISO 32000-1.