1) In a PDF file, the measure units are Inches. The page size is in inches. Any dimension is in Inches. There can be a bitmap having 200x200 pixels placed at 3x3 inches. Next to it can be a bitmap of 5x5 pixels placed at 5x5 inches.

That means, that PDF does not contain any DPI information. It is not needed at all. PDF rasterizer (e.g. a raster printer) can render it at any DPI. Photopea decodes and saves back bitmaps inside PDF in the original resolution. The rest is vector graphics.

2) For now, Photopea ignores embedded fonts. But it extracts the font name and in 98 % of cases, we already have the required font in our database of fonts, so we can render it identically.