Добавление файла в models.FileField.

from django.db import models
from django.core.files import File

#  Модель
class Uploaded(models.Model):
    file = models.FileField(upload_to='PATH')


# uploaded - Uploaded instance
with open(PATH_TO_FILE, 'rb') as file:
    uploaded.file.save('name', File(file))

uploaded.save()