code: public String getPageFromAnnotation(SNode node) {
      if (node != null && node.getAnnotations() != null) {
  
        Set<SLayer> layers = node.getLayers();
        String nodeNamespace = null;
  
        if(layers != null)
        {
          for (SLayer l : layers) {
            nodeNamespace = l.getName();
          }
  
          for (SAnnotation anno : node.getAnnotations()) {
  
            if ((nodeNamespace == null || input.getNamespace() == null)
                    && getPDFPageAnnotationName().equals(anno.getName())) {
              return anno.getValue_STEXT();
            } else if (nodeNamespace.equals(input.getNamespace())
                    && getPDFPageAnnotationName().equals(anno.getName())) {
              return anno.getValue_STEXT();
            }
          }
        }
      }
  
      return null;
    }
docs: Returns the value of page annotiation for a node. It takes the visualizer
  mappings into account. If no mapping is used, this definition is used: {@link
  #PAGE_NUMBER_ANNOATATION_NAME}