Hello @Hidden_Key_Group,
Please review this page with guidelines you can follow for posting questions.
On the surface, you might be able to use HighLevel LeadConnector Update an Opportunity module to add the PDF file.
Once you get this module added and set up, then you can report back to us any errors you received, screenshots of the module’s configuration, etc… that information will help us support you.
The module may ask for the data itself, or a public link to the PDF so that it can download it then upload it to the opportunity. We won’t know which way it needs until you try it out.
If you need help figuring out what it’s asking, then you can add the module then post screenshots of it.