To set an annotation style property such as color, interior color, border style, padding, etc to an annotation.

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

$circle = Circle::Create($doc->GetSDFDoc(), new Rect( 100.0, 100.0, 200.0, 200.0 ));
$circle->SetColor(new ColorPt(0.0, 1.0, 0.0), 3);
$circle->SetInteriorColor(new ColorPt(0.0, 0.0, 1.0), 3);
$circle->SetBorderStyle( new BorderStyle( BorderStyle::e_dashed, 3.0, 0.0, 0.0, array(2.0, 4.0)) );
$circle->SetPadding( 2.0 );
$circle->RefreshAppearance();
$page->AnnotPushBack($circle);

Add or edit PDF annotations sample
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).