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public class MultiPrintDocument : PrintDocument
        {
            private PrintDocument[] _documents;
            private int _docIndex;
            private PrintEventArgs _args;

            // constructors
            public MultiPrintDocument(PrintDocument document1, PrintDocument document2)
            {
                _documents = new PrintDocument[] { document1, document2 };
            }

            public MultiPrintDocument(PrintDocument[] documents)
            {
                _documents = documents;
            }

            // overidden methods
            protected override void OnBeginPrint(PrintEventArgs e)
            {
                base.OnBeginPrint(e);
                if (_documents.Length == 0)
                    e.Cancel = true;

                if (e.Cancel) return;

                _args = e;
                _docIndex = 0;  // reset current document index
                CallMethod(_documents[_docIndex], "OnBeginPrint", e);
            }

            protected override void OnQueryPageSettings(QueryPageSettingsEventArgs e)
            {
                e.PageSettings = _documents[_docIndex].DefaultPageSettings;
                CallMethod(_documents[_docIndex], "OnQueryPageSettings", e);
                base.OnQueryPageSettings(e);
            }

            protected override void OnPrintPage(PrintPageEventArgs e)
            {
                CallMethod(_documents[_docIndex], "OnPrintPage", e);
                base.OnPrintPage(e);
                if (e.Cancel) return;
                if (!e.HasMorePages)
                {
                    CallMethod(_documents[_docIndex], "OnEndPrint", _args);
                    if (_args.Cancel) return;
                    _docIndex++;  // increments the current document index

                    if (_docIndex < _documents.Length)
                    {
                        // says that it has more pages (in others documents)
                        e.HasMorePages = true;
                        CallMethod(_documents[_docIndex], "OnBeginPrint", _args);
                    }
                }
            }

            // use reflection to call protected methods of child documents
            private void CallMethod(PrintDocument document, string methodName, object args)
            {
                typeof(PrintDocument).InvokeMember(methodName,
                  BindingFlags.InvokeMethod | BindingFlags.Instance | BindingFlags.NonPublic,
                  null, document, new object[] { args });
            }
        }                    

1:

foreach (PrintDocument doc in documents) doc.Print();