A real PDF will be between 15 MB and 40 MB. If the file is 1 MB, it is low-resolution text that will pixelate when zoomed. If it is 100 MB, it might be an uncompressed scan that is slow to load. Aim for the 20-30 MB range for the sweet spot of clarity and speed.
Here is a typical layout of a high-quality PDF unit: comprehension orale 1 niveau a1 a2 pdf extra quality
The teacher’s guide or answer section is printed in small font. In low quality, answers become unreadable grey blobs. Extra quality preserves the contrast, so you can actually check your work. A real PDF will be between 15 MB and 40 MB