Open a PDF above and it reads every page, then tells you the lowest image resolution on each one. What you are looking for is the page with a number far below the others — that is where the trouble is.
Nothing is uploaded. The document is read inside your browser.
A PDF does not have a DPI
This is the thing almost every "check my PDF" answer gets wrong, and it is why a single number would be a lie.
A PDF is a set of instructions: put this text here, draw this line there, place this picture in that rectangle. The text and lines have no resolution at all — they are shapes, and they print as sharp as the press can manage at any size. Only the pictures inside have pixels, and each one has its own effective resolution:
the picture's own pixel count ÷ the size it was placed at
So the same image is 300 dpi in a thumbnail and 40 dpi stretched across a cover. The file did not change. The placement did.
That is why the answer here is per page and per image, and why "what dpi is my PDF" has no answer worth giving.
What to look for
Each page gets one line: the lowest resolution found on it. Not an inventory — a page can carry forty pictures and still have only one problem, and a list of forty is a way of not answering the question.
- 300 dpi or more — will print sharp at the size it sits at.
- 150 to 300 — noticeably soft up close, usually fine at a distance.
- Below 150 — visible to anyone.
- No raster images — the page is text and vector art. Resolution is not what will go wrong with it.
Where a low-resolution image usually comes from
Almost always the same three places:
- A logo pasted from a website. Screen logos are small on purpose. Ask for the vector — an SVG, EPS or AI — and it will print sharp at any size.
- A photo that has been through a chat app. Messaging apps re-compress. The version on the designer's disk is not the version in the PDF.
- A small image scaled up in the layout. Someone dragged a corner. The picture did not gain detail; it only got bigger.
What this reading can and cannot do
Printed on the page beside the results, because you should be able to check the answer rather than trust it:
- An image placed twice at two sizes is reported at its worst placement — the one that prints badly.
- A mask is measured as its own picture, because that is what it is.
- An image this tool cannot decode is reported as unread, and never as fine. If something is unreadable you will be told, not reassured.
- A page with no pictures has no resolution problem, and says so.
What it did not check
Resolution, and nothing else. Not bleed, not colour space, not embedded fonts, not overprint, not trim size. It makes no claim about whether the file is ready to print — only about whether the pictures inside it have enough pixels for the sizes they sit at.
Working with a single image instead
If you have a picture rather than a document, the image resolution checker answers the other half: how big that file can print, and whether the size you want will hold up.
When the file is not really the problem
Finding the bad image is the easy part. The expensive mistakes come later — a proof emailed round, three comments in a reply, a revision, and somebody approving a version nobody meant. That is what Proofavo is for: a proof link your customer opens without an account, comments pinned to the artwork itself, and a record of who approved what.