This post contains new and old manuals for Apple devices. If something is missing, let us know and we'll definitely add the manual or document you need to this section.
How to find out which firmware version you have? Go to Settings — General — About, there's a line: Software Version
All the most current manuals for iBooks (available for download on any Apple device) can be found at the link: https://books.apple.com/ru/author/apple-inc/id405307759#see-all/books
You can always download Adobe Reader for free from the official website:Adobe.com
Apple iPhone Documentation:
iPhone User Guide (For iOS 12)
iPhone User Guide (For iOS 11)
iPhone User Guide (For iOS 10)
iPhone User Guide (For iOS 9)
iPhone User Guide (For iOS 8.4)
iPhone User Guide (For iOS 7.1)
iPhone User Guide (For iOS 6.1)
Complete iPhone User Guide for iOS 5.1 (Russian)
Complete iPhone User Guide for iOS 4.2 and 4.3 (Russian)
iPhone 4S Product Guide
iPhone 4 Product Guide
iPhone 3GS Product Guide
iPhone 3G Product Guide
Apple AirPods Documentation:
AirPods (2nd generation) with Wireless Charging Case — Quick Start Guide
AirPods (2nd generation) with Wireless Charging Case — Safety and Handling
AirPods (2nd generation) with Charging Case — Quick Start Guide
AirPods (2nd generation) with Charging Case — Safety and Handling
Wireless Charging Case for AirPods — Quick Start Guide
Wireless Charging Case for AirPods — Safety and Handling
Apple Watch Documentation:
Apple Watch Series 4 Nike+ User Guide
Apple Watch Series 4 Hermès User Guide
Apple Watch User Guide for watchOS 5
Apple Watch Series 3 Nike+ User Guide
Apple Watch Series 3 Hermès Information
Apple Watch Series 3 Edition Information
Apple iPad Documentation:
Apple Pencil (2nd generation) — Quick Start Guide
Apple Pencil (2nd generation) — Safety and Handling
iPad User Guide (For iOS 12)
iPad User Guide (For iOS 11)
Complete iPad 1/2/3 User Guide (Russian)