【fix】【填写与签名】添加日期到文档上，复制并粘贴该日期，选中粘贴后的日期，属性面板显示为空

PDF Office/PDF Master/Class/PDFWindowController/PDFListView/CPDFKitExtensions/CPDFAnnotationExtensions/SelfSign/CSelfSignAnnotationFreeText.m

@@ -233,6 +233,10 @@
     }
 }
 
+- (id)copy {
+    return [[[self class] alloc] initPDFListViewNoteWithDocument:self.page.document subType:self.subType string:self.contents bounds:self.bounds];
+}
+
 #pragma mark - Init Methods
 
 - (id)initPDFListViewNoteWithDocument:(CPDFDocument *)document subType:(CAnnotationType)subType string:(nonnull NSString *)string bounds:(NSRect)bounds {