Addendum
I still have the file menu appearing 

and I can't see why.
Code:
<customUI xmlns="http://schemas.microsoft.com/office/2009/07/customui">
<ribbon startFromScratch="true">
<tabs>
<tab idMso="TabHomeAccess" visible="false"/>
<tab id="tabReportPrint" label="Report Print">
<group id="grpPrint" label="Printing">
<button id="btnQuickPrint"
label="Quick Print"
size="large"
imageMso="FilePrintQuick"
onAction="QuickPrintCallback" />
<button id="btnExportPDF"
label="Export as PDF"
size="large"
imageMso="FileSaveAsPdfOrXps"
onAction="ExportPDFCallback" />
</group>
</tab>
</tabs>
<!-- Empty QAT: greys out QAT strip and blocks customization -->
<qat/>
</ribbon>
<!-- Remove Backstage (File menu) options -->
<backstage>
<tab idMso ="TabPrint" visible="false"/>
<button idMso ="ApplicationOptionsDialog" visible="false"/>
<button idMso="FileExit" visible ="false"/>
<tab idMso ="TabOfficeFeedback" visible ="false"/>
<tab idMso ="TabInfo" visible ="false"/>
<tab idMso="TabInfo" visible="false"/>
<tab idMso="TabRecent" visible="false"/>
<tab idMso="TabNew" visible="false"/>
<tab idMso="TabOpen" visible="false"/>
<tab idMso="TabSave" visible="false"/>
<tab idMso="TabPrint" visible="false"/>
<tab idMso="TabShare" visible="false"/>
<tab idMso="TabHelp" visible="false"/>
<tab idMso="TabOptions" visible="false"/>
<tab idMso="TabClose" visible="false"/>
</backstage>
</customUI>