To add a sticky note (text annotation) to a PDF Document.

$doc = new PDFDoc($filename);
$page = $doc->GetPage(1);

// Create the sticky note (Text annotation)
$txt = Text::Create( $doc->GetSDFDoc(), new Rect( 10.0, 20.0, 30.0, 40.0 ) );
$txt->SetIcon( "UserIcon" );
$txt->SetContents( "The quick brown fox ate the lazy mouse." );
$txt->SetColor( new ColorPt(0.0,1.0,0.0) );
$txt->RefreshAppearance();
$page->AnnotPushBack( $txt );

Add or edit PDF annotations
Full code sample which shows how to add or edit PDF annotations (e.g. hyperlink, intra-document link, stamp, rubber stamp, file attachment, sound, text, free-text, line, circle, square, polygon, polyline, highlight, squiggly, caret, and ink).