Check that the specified file looks like a PDF

def can_import(self, file_uris, current_doc=None):
        """
        Check that the specified file looks like a PDF
        """
        if len(file_uris) <= 0:
            return False
        for uri in file_uris:
            uri = self.fs.safe(uri)
            if not self.check_file_type(uri):
                return False
        return True