A content block will apper asking you to provide a title, description and upload the PDF itself.
Also you have the option to embed the pdf file inside your sales quote. If you choose to embed the PDF file it will physically be added as additional pages to your sales quote. If you choose not to embed (ie a link is shown in your sales quote to open the PDF in a new browser tab).
You can attach as many PDF's as you like in every section of the sales quote, however be careful of adding too many as this will affect the file size of the sales quote when opened as a PDF by your customer.