Here are the steps to add a PDF to a Product in Magento 2,

Step 1. Install and enable the MageDelight's Product Attachments extension.

Step 2. Go to Catalog > Attachments Management > Add New Attachment.

Step 3. Choose the Attachment Type and enter the Attachment Name, Label

Step 4. Select the Customer group and upload the file.

Step 5. In the Attach To section, choose items to connect a new file to them.

Step 6. Save the changes.

Here are the few more resource to help you get most out of this Magento 2 Product Attachments Extension.

• How to Configure Product Attachments Extension in Magento 2
• How to Attach or Upload Product Descriptions File In Magento 2
• Build Customers Trust with Our All new Product Attachments Extension for Magento 2