an thus we will run out of space.

Wherever you put the PDFs, you still need enough disk capacity to store them!

If you're concerned about storing PDFs in the database because you may run out of space, it sounds like your operations need improving.

Storing in the Database

The biggest advantage is the files are consistent with the rest of the row data. When you insert/update/delete a row, you know the associated file was saved as expected.

When the files are outside the database, someone may (accidentally or maliciously) delete the files without changing the row. This leaves pointers to non-existent files!

Database backups include the files. While this makes the database backups (potentially a lot) bigger, it means you have everything when you recover. Remember you still need to backup the PDFs if you put them on the file system!

It's also easier to secure the files. If the PDFs contain sensitive data, you can use row-level security technologies such as VPD or RAS to restrict access.

Storing on the File System

It's easier to save the PDFs on cheaper storage.

You can access the files directly, without having to go through the database.

Both approaches work, but for me placing them in the database is a simpler solution. Think about how customers will access files after uploading them.

If you do decide to store the files outside the database, I suggest using BFILE. This is a locator for the file on the file system:

https://docs.oracle.com/en/database/oracle/oracle-database/20/sqlrf/Data-Types.html#GUID-3D9CC018-1637-45CB-95CF-DE67319D1A54