Open a PDF in iPad (IOS 10)

With iOS10 installed, you presumably have an iPad4.

The iPad4, along with other older 32-bit models of iPad, is fully obsolete. As all 32-bit Apps have been withdrawn from the Apple App Store, you'll not be able to download and install any Apps for your old iPad.

As such, unless existing Apps already installed on the iPad are sufficient for your needs, the iPad will have limited (if any) usefulness or utility.

You would be best advised to consider replacement with a much newer or current model iPad - that support iPadOS17. Of current models, even the entry-level iPad9 has specifications and capabilities that will massively outperform you current iPad - supports iPadOS17 - and is compatible with the vast majority of current Apps. Other models are more powerful still.

For information, here is a list of the highest version of iOS supported by the older models of iPad (for simplicity - “generations” are shortened to a number) that are restricted in their ability to be updated:

32-bit devices (obsolete)

iPad1 - iOS 5.1.1

iPad2, iPad3 and iPad mini1 - iOS 9.3.5 (WiFi Only models), iOS 9.3.6 (WiFi & Cellular)

iPad4 - iOS 10.3.3 (WiFi Only), iOS 10.3.4 (WiFi & Cellular)

64-bit devices

iPad Air1*, iPad mini2 and iPad mini3* - iOS 12.5.7

iPad Air2, iPad mini4 - iPadOS 15.8.1

iPad5, iPad Pro (9.7"/12.9" first generation) - iPadOS 16.7.5

(*) obsolete

Newer models are all able to be updated to the current version - iPadOS 17.3.1

• iPad Pro 12.9" (2nd generation and later)
• iPad Pro 11" (1st generation and later)
• iPad Pro 10.5"
• iPad Air (3rd generation and later)
• iPad (6th generation and later)
• iPad mini (5th generation and later)

Your iPad4 will not natively open a PDF file.

To reiterate - unless the iPad already has a suitable third-party App installed, you'll now be unable to install a compatible App from the App store. As such, your available options are limited.