public static class GdPictureExtension| GetCustomPDFInformations | Extract custom properties. No need to call GdPicturePDF.GetStat(). | 
| SetCustomPDFInformations | Update custom properties. No need to call GdPicturePDF.GetStat(). | 
| ThrowIfNotOk(GdPicturePDF, String) | |
| ThrowIfNotOk(GdPictureStatus, String) |