Insert file in database

Hello to all,
I am trying to upload a file in the mysql database, not just the name and store the file in my server. I would like to load a PDF file using bootstrap 4 form. The problem is that always give an error. The type of the field in the database is longblod. I did use that type before with PHP and always works fine. I saw a lot of help doing this process but are placing the file in the server and the name in the database only.
Thanks in advanced