check if file_exists() in uploads directory

This is a development site. I am trying to determine if a pdf file exists in the uploads directory. If so, I will provide a graphic and link, otherwise, I'll provide a grayed-out graphic.
This returns a negative:
$upload_dir = wp_upload_dir();
$upload_base = $upload_dir['baseurl'];
if (
file_exists( $upload_dir['baseurl'].'/pdfs/'.$prod_title.'-BR.pdf':wink:
) {
echo "The file exists!";
} else {
echo "File not found: $upload_base/pdfs/$prod_title-BR.pdf";
/*end code*/
The last line properly echoes the file path, and when pasted into the browser brings up the file, but the function returns a negative. Any ideas what I'm doing wrong? Thanks so much in advance!