Cognos how to hide pages/fields based on output format

create a render variable with ‘Expression Definition:’ as

ReportOutput () in ( ‘spreadsheetML’) –this would give output only for excel output report
ReportOutput () in ( ‘PDF’) — this would give specified output only for pdf output report.
ReportOutput () not in ( ‘PDF’) — This will hide specified output for pdf output report

Values that you could pass are:
items: [xlsxData, CSV, spreadsheetML, HTML, layoutDataXML, PDF, XML, XLWA, MHT, rawXML, XHTML, singleXLS, HTMLFragment]
case sensitive: true
Source:
https://www.ibm.com/support/knowledgecenter/SSEP7J_10.2.1/com.ibm.swg.ba.cognos.ug_md.10.2.1.doc/c_crx_reportoutput.html