Pdf and audio file download blocked by WAF on CDN

I have implemented WAF on CDN . When I download docx, excel file via CDN through android app , file is downloaded successfully and url looks like https://data.mydomain.com/doc_file

But when I try to download pdf and audio wav file via CDN though android app request, the file doesn't open and prompt message "Cannot be displayed " and url looks like http://data.mydomain.com/pdf_file. Http comes instead of https. But when I disable WAF file is downloaded from this link http://data.mydomain.com/pdf_file.

How to redirect Http to https for pdf download when accessed through CDN and WAF enabled? I have enabled Redirect HTTP to HTTPS in CDN behavior.