The ASPOSE document object is not searializeable.  In order to save the object to the database you first have to convert it to a memory from the object (such as PDF of Word). Once you have it in a Byte Array you can updated a BLOB column in the database.

//Convert to WORD
MemoryStream outStream = new MemoryStream();
asposeDocument.Save(outStream, Aspose.Words.SaveFormat.Doc);
byte[] docBytes = outStream.ToArray();

//Convert to PDF
outStream = new MemoryStream();
asposeDocument.Save(outStream, Aspose.Words.SaveFormat.Pdf);
byte[] pdfBytes = outStream.ToArray();