I had to deal with this thing too.
I disabled the native export menu from the toolbar and added a new button. The code I used to export the Word document with Specific Page Size is this:
Microsoft.Reporting.WinForms.Warning[] warnings;
string[] streamIds;
string mimeType = string.Empty;
string encoding = string.Empty;
string extension = string.Empty;
string deviceInfo =
"<DeviceInfo>" +
" <OutputFormat>Word</OutputFormat>" +
" <PageWidth>8.5in</PageWidth>" +
" <PageHeight>11in</PageHeight>" +
" <MarginTop>0.5in</MarginTop>" +
" <MarginLeft>0.5in</MarginLeft>" +
" <MarginRight>0.5in</MarginRight>" +
" <MarginBottom>0.5in</MarginBottom>" +
" <FixedPageWidth>True</FixedPageWidth>" +
" <AutoFit>True</AutoFit>" +
"</DeviceInfo>";
byte[] bytes = reportViewer1.LocalReport.Render(
"WORDOPENXML", deviceInfo, out mimeType, out encoding, out extension, out streamIds, out warnings);
using (FileStream fs = new FileStream("myreport.docx", FileMode.Create))
{
fs.Write(bytes, 0, bytes.Length);
}
Replace the "WORDOPENXML" with "Word" for .doc file export, as well as the filename "myreport.docx" to "myreport.doc"