About converting a PDF to images
When converting to images is the right move
The commonest reason is that the other side can only take images. A chat window previews a picture inline while a PDF has to be opened as an attachment; social posts accept images in the body and nothing else; online forms often allow only JPG or PNG. The second reason is moving content into another document: dragging a chart into a slide or a report is simplest as an image, and the layout cannot shift on someone else's machine. The third is thumbnails and cover art — a preview of the first page next to an entry in a list.
PNG or JPG?
It depends what is on the page. For pages that are mostly text, tables and vector charts, choose PNG: it is lossless, so strokes and hairlines do not turn into smudged blocks and the edges stay clean when you zoom in. For pages that are mostly photos or scans, choose JPG: at the same apparent quality it is usually a fraction of the size, and a photograph has no crisp edges that need protecting anyway. If you are unsure, export one page with the default PNG and look at it, then switch if it is wrong — the conversion happens in your browser, so trying a few times costs nothing.
Which resolution to pick
PDF page sizes are measured in points, one point being 1/72 inch, so a 72 DPI export has exactly as many pixels as the page has points — the page at its native on-screen size. For everyday sharing 150 DPI is plenty; for printing, or for further editing in an image editor, choose 300 DPI. Beyond that there is little to gain: a low-resolution scan inside the PDF does not get any sharper because you exported at a higher DPI, it only makes the file bigger. Browsers also cap how many pixels a single canvas may hold; past that limit this tool steps the resolution down and says on the page what DPI it actually used, rather than quietly handing you a blank image.
Once it is an image, the text is gone
This is worth settling before you start. Text in a PDF is a text object: it can be copied, searched, and read by search engines. Once the page is an image those words are pixels — not selectable, not searchable, and Ctrl+F finds nothing. Images are therefore good for "someone will look at this" and bad for "we may need to search this later". If your aim is to stop people copying the text, converting to images does work, but notice the flip side: you will not be able to search it either. When the text layer matters, do not convert — send the original PDF.
If what you want is precisely that text — quoting a passage, pasting the content into your notes, searching for keywords, feeding it to another program — then converting to images is the long way round. Use Extract Text from PDF to pull the text layer out directly, with an optional page range and one-click copy or .txt download. The dividing line is clear: if you want the layout, convert to images; if you want the text content, extract text. There is one case neither helps with: the source file is a scan to begin with, every page is an image with no text layer, and text extraction then returns an empty result and tells you exactly why — recognising that needs OCR, which this site does not provide.
How this differs from the other operations
Converting to images re-renders the whole page picture; the page count does not change and one page gives one image. If a single page holds two pages' worth of content — a book scanned across the spread, an exam paper imposed on A3 — the layout has to be cut apart first, which is what Split PDF Pages does; convert after cutting and you really do get one image per page. To join several PDFs into one, or pull out a few pages by number, use Merge PDF. The other way round — you already have a pile of images and want them bound into one PDF — use Image to PDF.