Is it possible to make a HTML page behave, for example, like a A4-sized page in MS Word?
Essentially, I want to be able to show the HTML page in the browser, and out
PPI and DPI make absolutely no difference to how a document will print off a browser. the printer takes no information on screen dot pitch or the DPI of the images etc. if you are printing images they would print at a size similar in proportion to how they are displayed on screen. the print processor of the browser would increase the DPI of the images from something rather low like 72dpi to whatever DPI the rest of the document is. say the image displays as half a page wide, then its about 4" wide physically. the pixel width of the image would be approx 300px to display correctly in the browser. by the time it prints at a nominal 300DPI, the processor has added pixels and the image will grow to around 1200px which at 300 DPI is 4".
when it comes to vector or non pixel based elements like text, the printer chooses its own DPI from the driver which doesnt relate to screen dot pitch or browser width etc. if the browser is 3000px wide, the print processor will wrap text as appropriate.
heres what makes it hard about creating print displays: each browser and printer will interpret text sizes (pt, em, px) and spacing in its own way. depending on what printer, browser and maybe even OS you use, you will get a different amount of lines and characters per page. so even if you test on your computer using your browser and printer and figure out that you can display the text in a box at 640x900px and its perfect on print, the next guy who tries to print will possibly get it printing differently. there really is no way to force each printer and browser to get it identical each time.
forget pixels and moreso forget DPI, the only thing you could use pixels for is setting a table width that simulates the width of a printable area on your printer. in that case i found that 640px wide is close.