I just bought a used iPhone 8, my first Apple product.
There is an iPhone User Guide from Apple. My normal practice with user manuals in electronic form is to download them in a standard, widely supported file format (almost universally PDF), and save this permanently into my LAN fileserver (which runs Solaris and serves SMB to Windows clients).
With just about any other manufacturer on the planet, for any product from an Earth station antenna control system to a toaster, this would have been a dead-simple matter of vising their website using any standards-compliant web browser on a computer running any operating system, locating the manual's download link, and using the browser's "Save As" function.
This is proving to be a little more complicated in this particular case. I did find a web page that tells me the document exists, but seems to be devoid of any link to it:
https://books.apple.com/book/id6443146864
It seems that I must access it through the proprietary "Apple Books" portal. After reaching more Apple web pages that were devoid of anything actionable, I somewhat concluded that my only way of accessing this is through the iPhone itself. (I'm slightly curious as to whether these web pages would do anything on a Mac...)
After some Apple ID rigmarole and then tapping on a "Get" button that did absolutely nothing, I finally found that if I instead opened a sample of the book, the "Get" button at the top of the sample actually worked, albeit only after setting up an iTunes account.
So now, the manual is in some manner in the iPhone. I'm able to flip through its pages in the iPhone. But I still want it as a PDF, EPUB, or other standard file on my fileserver. I'm not sure how much closer this brings me. I did find this tip:
https://discussions.apple.com/thread/7514400?answerId=30001597022#30001597022
It mentions that, due to DRM, books can't be read on non-Apple systems unless they're free. But this one is free, so that shouldn't be an issue. The thread also says:
To redownload actual ibooks, go to the Purchased link under Quick Links on the right-hand side of the iTunes Store homepage
So I install iTunes into a Windows VM, log into it using the same Apple ID I had used on the iPhone, find "Purchased" under "Quick Links", and then select the "Books" button at top right. The main window area just displays "You do not have any purchased books available to download."
Another idea was to try to get the iTunes Store in the iPhone to save it into some well-defined location in the phone's storage, from which I could copy it out. I tap "More" and there is a "Purchased" menu item, but going into that, I see only Music, Movies, and TV Shows categories. Nothing about books.
This other question has some answers but they look like they apply to Macs, not iPhones:
Locating the iBooks folder in iCloud Drive
I tried connecting the iPhone to a PC via USB, just to see what I could find. The Internal Storage directory exposed via MTP has a DCIM folder for the camera, but nothing else. In principle maybe I could first copy the document from wherever the Apple Books app has it cached into the Internal Storage directory, but I'd need access to the phone's underlying filesystem. There's a "Files" app, but it seems to have no meaningful access to the actual filesystem. The "On My iPhone" category is empty, but the phone is obviously not empty, or it wouldn't boot.
I've even taken the unprecedented step of searching torrent sites for the official user manual of a consumer product. No luck.
Is it even possible, given just an iPhone plus non-Apple systems, to obtain the iPhone User Guide as a computer file under my control? If so, how would I go about doing this?
If the only solutions would involve jailbreaking the iPhone, I'd have to hold off on it for a little bit until it has a replacement, in case it gets bricked.
