iPhone,iPad iPod touch用アプリをランキング掲載！ レビューを分析して日本で人気のあるiPhoneアプリを見つけられます。

This is a simple but powerful PDF viewer for your Apple Watch.

Having PDFs on your Apple Watch gives you following benefits
1. Convenience: Having PDFs on a smartwatch allows for easy access to important documents without having to pull out a phone or computer. This can be especially useful for people who are always on the go.
2. Quick reference: PDFs on a smartwatch can be used as quick reference guides for things like recipes, instructions, or presentations. This can be helpful for people who need to quickly look up information while they're away from their main device.
3. On-the-spot Decision Making: In a meeting or a presentation, having PDFs on smartwatch can be helpful for taking quick notes, making decisions and take actions on the spot.

The iPhone app has a simple user-friendly PDF converter integrated so that you could create PDFs easily.
Using iPhone app you could create PDFs from Photos & Scans. 
You could also import your existing PDFs from Files app.