Is your screen suitable for pdf reading?
From the Guardian: What’s the best cheap tablet or e-reader for PDF files?For your purposes, the best screen size would be 210 x 297mm, which is the same as A4 paper. This has a diagonal of 14.3in, so a 14in screen would be closest to life size. However, a 12.3in to 13.3in screen should be perfectly acceptable.
The other key point is the aspect ratio of 1:1.414. Since you can’t get A4, the best match would be a device with a 3:2u> screen, such as a Microsoft Surface Book or a Google Pixelbook. These screens have an aspect ratio of 1:1.5.
The next best would be either 4:3 (1:1.333), which was used by traditional TV sets, or 16:10 (1:1.6), as used by, for example, Apple’s MacBook Pro. The 4:3 format lives on in screen resolutions from 640 x 480 (VGA) to 1440 x 1080 and 1920 x 1440, while 16:10 resolutions include 1440 x 900, 1920 x 1200 and 2560 x 1600.
Unfortunately, the cheapest screens are 16:9 widescreens, which is partly why they are used in cheap laptops. Their 1:1.778 aspect ratio is not a good fit for A4’s 1:1.414. You could try viewing some PDF files on a 1920 x 1080 aka Full HD screen to see if it meets your needs.
Height: Width: Screen size (e.g. 10.1, 11.6, 14, etc.):