Django Reportlab generates empty pdf

I'm using reportlab to create a pdf. I am using Reportlab Paragraphs. The problem is everytime i download it, it generates an empty txt. I tested it without django and it works without a problem. If i'm using canvas it works but it doesn't suit what i need.

views.py

from django.http import HttpResponse
from django.shortcuts import render
from reportlab.lib.enums import TA_JUSTIFY
from reportlab.platypus import SimpleDocTemplate, Paragraph, Spacer
from reportlab.lib.styles import getSampleStyleSheet, ParagraphStyle
from reportlab.lib.pagesizes import letter


def genereaza_pdf(request):
    if request.method == 'POST':
        response = HttpResponse(content_type='application/pdf')
        response['Content-Disposition'] = 'attachment; filename="example.pdf"'
        doc = SimpleDocTemplate("example.pdf", pagesize=letter, rightMargin=70, leftMargin=70, topMargin=70,
                                bottomMargin=60)
        report = []

        styles = getSampleStyleSheet()
        styles.add(ParagraphStyle(name="Times", fontName='Times-Roman', fontSize=15, alignment=TA_JUSTIFY))

        p_text = "<u>ANEXA 1</u>"
        report.append(Paragraph(p_text, styles["Times"]))
        report.append(Spacer(1, 5))
        doc.build(report)
        return response
    return render(request, 'pdf_test.html')

pdf_test.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Download pdf</title>
</head>
<body>
    <form method="POST">
        {% csrf_token %}
        <button type="submit">Download</button>
    </form>
</body>
</html>

What seems to be the problem?

Solution

The function was generating two files, one in Downloads as default but it was an empty txt and one in the project's directory. I've made the changes.

def genereaza_pdf(request):
    if request.method == 'POST':
        response = HttpResponse(content_type='application/pdf')
        response['Content-Disposition'] = 'attachment; filename="example.pdf"'
        doc = SimpleDocTemplate(response, pagesize=letter, rightMargin=70, leftMargin=70, topMargin=70,
                                bottomMargin=60)
        report = []

        styles = getSampleStyleSheet()
        styles.add(ParagraphStyle(name="Times", fontName='Times-Roman', fontSize=15, alignment=TA_JUSTIFY))

        p_text = "<u>ANEXA 1</u>"
        report.append(Paragraph(p_text, styles["Times"]))
        report.append(Spacer(1, 5))
        doc.build(report)
        return response
    return render(request, 'pdf_test.html')