You would use optical zoom. Optical zoom is controlled, most often, using manual controls (dials/knobs) on the projector.

Digital zoom would be in the menu of the projector.

Not sure what specific projector you are using, but the quality of the image is often directly in proportion to the quality of the unit itself. Anything higher than about 1080p (1920x1080) native resolution of the projector is wasted when reading text. The text will be too small to read easily at 4K resolution.

Quote (doctort on Nov 12, 2022 5:55 AM): I want to read the large text clearly on the screen of the projector for avoiding the eye strain. I should purchase the expensive projector for reading the large text with good quality or resolution?

If your intent is to use this for hours a day, then spending a bit more will help with reliability some. Epson has good 1080p projectors, like their 2150 or their 3200/3800 models which are good, but if you aren't DLP Rainbow susceptible, then BenQ is the way I would go. Probably get their X1300i LED projector which is plenty bright and very sharp.