Make no mistake - most of these devices won’t be used as pdf readers - they will end up in the landfill. This is part of the business model, and we + the environment pay for it.
I have 7 Macs that I use to operate 3 businesses (and 2 more by way of consulting); precisely none of them use the App Store.
1. The security issue i mentioned earlier applies to macs. It’s a bit easier to mitigate because an older mac can run a newer non-system-linked browser. But e.g. firefox is dropping support for 10.14 (released in 2018) this year (https://support.mozilla.org/en-US/kb/firefox-users-macos-101...)
2. If you keep your os up to date as long as possible, new features will drag performance down to the point of being nearly unusable. So you’re forced to tradeoff between security+features and performance.
Of course, with a old mac you can always install linux to extend its lifespan… but that’s not thanks to apple
The iPad 3rd generation was released in 2012, so the 2016 9.3.5 iOS release gave 4 years of security/bugfix support for the WiFi-only version of that device.
Which means there is a decent chance an iPad running 9.3.2 is vulnerable.
And there have been thousands of CVEs since 9.3.2. Most of low severity, but not all.
This is in a lot of the reporting about the topic and linked repeatedly in these comments. Please don't repeat false information.
Now you're right that this particular really old version also doesn't get security updates - but boy do I not have that expectation, and I would be surprised if anyone acting in good faith did.