string gdbpath = @"E:\newShapes.gdb";
            FileGeoDatabaseFeatureLayer.CreateFileGeoDatabase(gdbpath);
            Collection<FeatureSourceColumn> columnsTemp = new Collection<FeatureSourceColumn>();
            columnsTemp.Add(new FeatureSourceColumn("myblob", "blob", 1));

            FileGeoDatabaseFeatureLayer.CreateTable(gdbpath, "Table1", WellKnownType.Point, columnsTemp);

            FileStream pdffile = new FileStream(@"e:\yourpdf.pdf", FileMode.Open);
            byte[] bytes = new byte[(int)pdffile.Length];
            pdffile.Read(bytes, 0, (int)pdffile.Length);
            pdffile.Close();

            FileGeoDatabaseFeatureLayer gdbLayer = new FileGeoDatabaseFeatureLayer(gdbpath, "table1");


            string newString = Convert.ToBase64String(bytes);
            Feature feature = new Feature(0, 0);
            feature.ColumnValues["myblob"] = newString;
            gdbLayer.Open();
            gdbLayer.FeatureSource.BeginTransaction();
            gdbLayer.FeatureSource.AddFeature(feature);
            gdbLayer.FeatureSource.CommitTransaction();

            Collection<string> ids = new Collection<string>() { "1" };
            Feature f = gdbLayer.FeatureSource.GetFeaturesByIds(ids, ReturningColumnsType.AllColumns)[0];

            byte[] tempBytes = Convert.FromBase64String(f.ColumnValues["myblob"]);

            FileStream fileStream = File.Create(@"e:\b.pdf", tempBytes.Length);
            fileStream.Write(tempBytes, 0, tempBytes.Length);
            fileStream.Close();