All Apple devices — including iPhone — come with a native e-book reader app called Books. This app supports PDF format in case you have a number of books in PDF and want to read them on your iPhone. Unfortunately, on iPhone, adding a new PDF file to the Books app is not as easy as reading the book itself. In fact, you can’t add a new PDF file on the Books app o iPhone at all.
So, what if you want to read new PDF books on your iPhone?
As you know, Apple — and most tech companies — uses the cloud technology to make the synchronization between devices. In the case of Apple, the technology is iCloud. In the Apple ecosystem, the data you add to a certain app via a certain device (e.g., MacBook) can be accessed on other devices (e.g., iPad and iPhone) as long as you use the same Apple account on each device.
In other words, when you add a PDF file to the Books app via MacBook, it is also accessible on the Books app on iPhone as long as the Apple account you use on MacBook is the same as the one you use on iPhone.
Adding PDF Files to the Books App via MacBook
To add a PDF file to the Books app via MacBook, first, launch the Books app from Launchpad. Next, select the PDFs menu on the left panel.
Drag the PDF file you want to add from Finder to the Books app.
Wait a moment until the PDF is done being imported.
Adding PDF Files to the Books App via iPad
If you have iPad as well, you can also add a new PDF file to the Books app via your iPad. First, launch the Books app on your iPad and go to the PDFs menu. Next, click the three-dot icon at the top your screen and select Slit View.
Open the Files app (or cloud storage app depending on where you store your PDF file) and drag the file to the Books app.
Accessing the PDFs on iPhone
As mentioned earlier above, all PDF files you added to the Books app from a certain Apple device can be accessed on the Books another Apple device as long you use the same Apple icon each device.
That being said, to access the PDF files you have added via MacBook and iPad above on your iPhone, first, launch the Books app on your iPhone. Tap the user icon on the top-right corner to login with your Apple account. Just make sure to login with the same Apple account as the one you use on MacBook and iPad.
Once logged in, go to the PDFs menu on your Books. You should see the newly added PDF files up there.