Would you please provide more details about the problem so that we can troubleshoot it?
Are you trying to view your bank statement (in the PDF format) in Safari (built-in web browser) on your iPhone?
Do you see an error message? What is the error message? Does it actually say that you need a PDF reader to view the bank statement?
Would you post the screenshot of the error message (not your bank statement) to your next forum reply?
If nothing happens when you tap the link or button in a web page to open your bank statement, you may want to temporarily turn off the "Block Pop-ups" option (iOS Settings > Safari > Block Pop-ups) and try again.