Hi @Mailing_ODYSSEE 
Welcome to the community 
With the Gmail node, you’ll need to ensure you have Download Attachments toggled, like this:
A workflow with a pdf and the Extract from file node would look like this:
From there, the contents of the PDF are extracted as JSON, so it’s usable in further nodes.
Can you share your workflow with us so we can see a bit more about what you’re doing? 