Error to merge PDFs with PdfDocumentBase.Merge method - Length cannot be less than zero

Stack trace - when try to generete PDF From 2 forms with Marge Method

System.ArgumentOutOfRangeException: Length cannot be less than zero.

Parameter name: length

at System.String.CtorCharArrayStartLength(Char[] value, Int32 startIndex, Int32 length)
at Syncfusion.Pdf.IO.PdfLexer.YyText()
at Syncfusion.Pdf.IO.PdfParser.ReadUnicodeString()
at Syncfusion.Pdf.IO.PdfParser.Simple()
at Syncfusion.Pdf.IO.PdfParser.ReadPair()
at Syncfusion.Pdf.IO.PdfParser.Dictionary()
at Syncfusion.Pdf.IO.PdfParser.Simple()
at Syncfusion.Pdf.IO.CrossTable.GetObject(IPdfPrimitive pointer)
at Syncfusion.Pdf.IO.PdfCrossTable.GetObject(IPdfPrimitive pointer)
at Syncfusion.Pdf.Primitives.PdfReferenceHolder.get_Index()
at Syncfusion.Pdf.Primitives.PdfReferenceHolder.GetObject()
at Syncfusion.Pdf.Primitives.PdfReferenceHolder.get_Object()
at Syncfusion.Pdf.IO.PdfCrossTable.GetObject(IPdfPrimitive pointer)
at Syncfusion.Pdf.Interactive.PdfLoadedBookmark.GetNext()
at Syncfusion.Pdf.Interactive.PdfBookmarkBase.ReproduceTree()
at Syncfusion.Pdf.Parsing.PdfLoadedDocument.get_Bookmarks()
at Syncfusion.Pdf.Parsing.PdfLoadedDocument.CreateBookmarkDestinationDictionary()
at Syncfusion.Pdf.PdfDocumentBase.ImportPageRange(PdfLoadedDocument ldDoc, Int32 startIndex, Int32 endIndex)
at Syncfusion.Pdf.PdfDocumentBase.Append(PdfLoadedDocument ldDoc)
at Syncfusion.Pdf.PdfDocumentBase.Merge(PdfDocumentBase dest, Object[] sourceDocuments)