How Do I Change the Size Of Text In a PDF File?

I enjoy reading PDF files on my iPhone. I usually save them in iCloud Drive so I can read them on any device. The PDF files look great on my MacBook Pro and iPad, but I often have to pinch to zoom to resize the text on my iPhone. Unfortunately this forces me to scroll horizontally from sentence to sentence. How do I change the size of text in a PDF file without having to scroll horizontally on an iPhone? The code responsible for reading a PDF file should allow for re-rendering like a web browser does (configuring viewport), but this doesn’t seem to be the case.
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Ian MacGregor