Go to Settings and then click on General. You will see Mandatory Quote Upload under Financial Settings. Turning this switch on will force users to upload a quote pdf for quotes to then generate a purchase request. When you toggle this on the pop up will appear 'Your changes have been saved! Mandatory Quote Upload is switched on'.
Once the Mandatory Quote Upload is switched on. Admin users now must upload a pdf quote file in order to progress to the Purchase Request details page.
Below is a video link to view this new feature.