drik

Not sure what you mean by "FX style"
If it is a layer FX, tick on the FX icon on the layer and untick the effect.
If you just mean a style (Styles panel) try Edit > Defaults > Revert

Indeed. Thank you Walt 🙂 
Note: For anyone else reading, the lines will not be there in the exported file.
 

If you're talking about the blue frame around the top text, that's probably View > Show Text Flow.

Welcome to the Affinity forums @RomanaS!
Have the Move Tool selected, click Spread Setup from the top toolbar, change the Page Preset to US Letter, visit then the Scaling tab, select Rescale and click OK. Please note, that the ratios between A4 and US Letter are different, so you have to adapt your layout a bit (I guess).

This short video is about how to create offset paths in Affinity Designer.  Offset paths are a powerful tool that designers use to create exact duplicates of a vector object shape and then use these duplicate as individual vector objects.  With the ability to create an exact size for your offset, you've have a powerful tool to create fantastic eye catching layers in you digital art. Creating offset paths in Affinity Designer is quick and it's easy. I show you how to setup the keyboard shortcut and with one click you are ready to create offsets for any object, shape, text, or line.  Offset paths are one of the secrets that designers use to create stunning computer graphics.  Create your own website graphics, digital art, blog posts illustrations, instagram images, and go ahead and brag on twitter!  Happy Creating :-) Jen
 

I am adding this so someone can find it . I am no expert at this
Load a Photo
From the adjustments tab
Turn it black and white Invert it Go to the layers tab and change the blend mode from normal to "lighten"
If you still have dark areas, select them and adjust them as needed in a new layer
Some add a touch of blur to the lines to soften them. I don't particularly car for that but by all means try it
UPDATE: If you really want sketches and / or coloring pages the best answer comes from an Affinity Revolution tutorial
 

For Apple users like me, Pages has ePub conversion. I used it before for a 250 page book and it worked fine for Kindle, Apple, Google, etc. I have had a book that sells among the top for its genre for several years using this ePub. The only glitch is that Pages has only a TOC, but not an index function. I built the index from scratch with bookmarks. I'm considering Affinity for the PDF version for print functions, (TOC, index, and bleed), since  Apple Pages doesn't have index or bleed, only TOC. So for the price of Affinity,  this all sounds good, but then for ePub, I may copy the book back into Apple Pages for the Epub. I don't know what'll happen to the index. Perhaps some of the formatting will hold and I won't have to build the index in ePub from scratch. I use InDesign for covers, but haven't tried it for the book interior, and Affinity looks less complicated than InDesign, so I may give that a try. For $50, it's worth a try.  

There used to be a Painting category, back in Designer 1.6 in the Pixel Persona. I don't know if it was in Photo, and I don't think it has existed since the restructuring of brushes that was done in 1.7. Additionally, since then Serif did additional restructuring and even modification of the brushes in 1.8.
But you can find the old 1.6 brushes from Designer here: https://www.dropbox.com/sh/gkm6n0lopdon4yk/AAByJcQ7o3eMrD1izyVqlknMa?dl=0
 
 

Probably you used to do 8-bit images in PSE, but AP defaults to 16-bit.