You have to enable high-quality zooming. To do this, open your score, tap the center of the screen to bring up the song overlay, tap the second icon at the bottom left, then "Zoom/Pan Settings". You can then check the option to enable high-quality zooming which will re-render the PDF if you zoom in and release. If the PDF renders quickly, this works fairly well. If it renders slowly, then it will be a more jarring experience, depending on your workflow. By default, MobileSheets just zooms in on the image without re-rendering it at a larger size, as this is faster and uses less memory. I don't do tile-based rendering (where only the zoomed in portion of the page is re-rendered), so when the page is enlarged with high-quality zooming, a much larger bitmap is generated at the new zoom level, which renders slower and uses more memory. I am going to explore the possibility of doing tile-based rendering in the future (to get the best of both worlds as you typically see in most PDF viewers), but it will require significant changes to the way zooming and rendering works.
Mike
Mike