A page is rendered, not extracted as a document
PDF pages may combine text, vectors, images, fonts, and annotations. PNG represents a rectangular grid of pixels. Rendering a page therefore changes the nature of the content: text is no longer selectable as text in the image, and vector edges are sampled at the chosen resolution.
Use PDF to PNG for previews, slides, or graphics that need a raster asset. Keep the PDF when searchable text, selectable elements, links, or exact page geometry matter. A PNG preview is convenient, but it does not replace the structured source document for editing or accessibility tasks.