Please check the whether file exists at the mentioned path for this, to check whether the file exists or not please us the file exists activity and pass the output of that variable into the if condition and if exists then do the necessary activities in the then block.
In the wait for download activity, under ignore temporary file extensions insert “tmp” to ignore the downloaded file if its tmp extension. Then using file exists you can check if the file is downloaded or an if statement that checks if downloaded file variable extension is pdf