If your requirement is to export the report in Landscape mode, then you need to set the page orientation as “Landscape” at report design level from Report Properties. If you still face any issue, then share your RDLC report with us to validate the problem at our end.
We have validated your shared report and in that the page orientation is specified as Portrait only, so we have modified the page orientation as Landscape and it has been exporting properly as PDF in Landscape. Please find the modified report from the below location.
If you still face any issue, then please share the Syncfusion product version you are using with us for further validation.