Thank you for reaching out to the Community for assistance!
To link a PDF to an e-form, first, you will want to upload the resource. Navigate to Configuration > Resources > Add Resource to browse and name the uploaded file.
Now edit your E-Form under Configuration > E-forms. Then add a new question to the form and choose the Library Resource question type, pick the uploaded resource, and it will display on the e-form as a downloadable link once assigned. Once the new question is added to the e-form, hit Save Final.
Please let us know in case of further queries.