According to a tweet by Affinity by Serif, the December 2018 issue of the Practical Photography Magazine has a free 32-page Affinity Photo Editing Guide.
From the screenshot
Get a 32-page Affinity Photo Editing Guide free with the latest issue of Practical Photography, the UK’s best selling photo magazine. Contains six complete guides to core skills and everything you need to get started straight away – on sale now https://www.practicalphotography.com/ @practphoto
