The pdf-to-png tool hardcodes a 300 dpi rendering resolution through Ghostscript's -r300 flag, with no dpi field on the page.
Adobe notes that its free online PDF-to-PNG converter does not offer manual DPI selection, unlike the desktop Pro app which exposes a DPI dropdown. PDF to PNG - how to convert PDF files to PNG online - Adobe Acrobat
PDF To PNGPDF To PNG Resolution DPI
The pdf-to-png page offers only a choice between converting all pages and converting selected pages before rendering starts.
Select the PDF file you want to render as images.
Select the option to convert all pages or specific pages.
Checking Pixel Dimensions Against Source Size
Download the resulting PNG image.
Compare the image pixel width against the source PDF page width.
Compare the image pixel height against the source PDF page height.
Continue with PDF to PNG Large File Size or PDF to PNG Corrupted PDF Fails.
Frequently Asked Questions about PDF To PNG Fixed Resolution DPI
Can I raise the resolution above 300 DPI?
Zoom into a separate image editor after downloading for extra detail.
How do I convert a second document afterward?
Refresh the page and add the next PDF file.
Where do the converted images get saved?
Check your browser's default downloads folder.
How do I confirm the DPI used for the output?
Open the PNG's file properties to view its pixel dimensions.