File Not Found Error in Python Flask for pdf input to excel output

Question

I'm writing a program that reads pdf and return an excel sheet using flask python. I keep getting File Not Found error in html web page.

from PyPDF2 import PdfReader, PdfWriter
DOWNLOAD_FOLDER = os.path.dirname(os.path.abspath(__file__)) + '/downloads/'
app.config['DOWNLOAD_FOLDER'] = DOWNLOAD_FOLDER
app.config['MAX_CONTENT_LENGTH'] = 8 * 1024 * 1024

@app.route('/uploads/<filename>')
def uploaded_file(filename):
   return send_from_directory(app.config['DOWNLOAD_FOLDER'], filename, as_attachment=True)

def process_file(path, filename):
   toExcel(path, filename)

def toExcel(path, filename):
    input_file = PdfReader(open(path, 'rb'))
    output = PdfWriter()
    page_nos = len(input_file.pages)

I tried using validation of the input file, but didn't work

The correct output should return processed excel sheet.