I am new to Affinity having to replace an older version of Photoshop and I've never had this problem with Exporting PDF's. In Affinity I was only able to export one photo to PDF. The next photo was unable to be saved as a PDF. Like others who had the same issue I feel this is a weakness of Affinity. Since I need the PDF's for a job, I'm going to have to find someone who has a version of Photoshop or buy the latest version to complete my job.