Adding a PDF to a sqlalchemy database

I have a simple model that I want to store the binary contents of a PDF file in a data attribute:

from app import db

    class Model(db.Model):
        id = db.Column(db.Integer, primary_key=True)
        data = db.Column(db.PickleType, nullable=True)

I'm trying to add some arbitrary PDF file to the data attribute as follows:

@app.route('/')
def index() -> str:
    model = Model.query.get(1)
    model.data = open('./app/static/pdf/file.pdf', 'rb')
    db.session.commit()
    return ''

But I'm getting the following error:

sqlalchemy.exc.StatementError: (builtins.TypeError) cannot serialize '_io.BufferedReader' object
[SQL: UPDATE model SET data=? WHERE model.id = ?]
[parameters: [{'data': <_io.BufferedReader name='./app/static/pdf/file.pdf'>, 'model_id': 1}]]

What is the correct way of doing this, please? How should I go about serializing a PDF file?

Thanks for any help :-)