ICO to PDF Converter

1Drop your BMPs inIt never leaves your machine.

2Set the pageEverything updates as you change it.

3Build and downloadAssembled here and saved from your own browser.

Very large in, very small out

A bitmap stores every pixel uncompressed, which is why these files are enormous. Re-encoding on the way in typically turns megabytes into kilobytes with no visible difference.

How to use this tool

Drop one or more icon files on the box at the top. Every size inside each file is listed, with the one being used marked, so you can see exactly what the file contained before anything is built.

Set the page and the margins as you would for any image, then build the PDF.

One icon file, several pictures

This is the part most converters ignore, and it is the reason the results are often disappointing.

An ICO file is a container rather than a single image. It holds a set of pictures at different sizes so the operating system can draw a crisp icon in a toolbar, in a file list and on a desktop without scaling anything. A typical file holds sixteen, thirty two and forty eight pixel versions, and a modern one usually adds two hundred and fifty six.

Hand that file to a browser and it decodes one of them and hands it back, and which one you get is not something you chose. A converter built on that behaviour can quietly give you the sixteen pixel version of an icon that also contained a two hundred and fifty six pixel one.

So this reads the directory inside the file first, lists everything it finds, and lifts out the one you asked for.

The zero that means two hundred and fifty six

Each entry in the directory records its width and height in a single byte each, which can only count to two hundred and fifty five. The format solves that by treating zero as two hundred and fifty six.

It is a small detail with a large consequence. Software that reads the byte literally sees a picture zero pixels wide, decides it is empty, and skips the largest and best image in the file. That is checked here, and a two hundred and fifty six pixel entry is correctly reported as the biggest thing present.

A worked check you can repeat

Drop a Windows application icon in. The list shows every size the file holds, the largest is marked as the one being used, and the finished PDF contains that version rather than a toolbar sized one.

Switch to the smallest and drop the same file again. The marked entry moves, and the image in the preview is visibly coarser, which is the difference the choice actually makes.

The reading of the container was checked against an independent implementation before publishing: twenty five hand written cases covering single and multiple sizes, the zero that means two hundred and fifty six, PNG and bitmap payloads, cursor files, and every malformed header that should be refused. Then forty thousand generated files, of which nearly thirty five thousand held more than one size, confirming that every entry is validated against the real length of the file and that the largest is always correctly identified. Two hundred pieces of random rubbish were refused rather than parsed.

Mistakes that catch people out

Expecting an icon to print sharply. Even the largest version is small. Icons are made for screens, not paper.

Changing the size and not dropping the file again. The choice is applied when the file is read, so reload it after changing.

Assuming every icon holds a large version. Plenty of older ones stop at forty eight pixels. The list tells you before you build.

Renaming a PNG to have an icon extension. That does not make it an icon, and the file will be refused with a reason.

Common questions

Is my icon uploaded anywhere?

No. The file is read by your browser, the PDF is built here on the page, and the download comes from your machine. Nothing crosses the network.

Why does one icon file contain several images?

So the operating system can show a crisp icon at any size. A single file typically holds sixteen, thirty two and forty eight pixel versions, and often a two hundred and fifty six pixel one as well.

Which size does this use?

The largest in the file by default, because that is the one that stays sharp on paper. You can switch to the smallest, and every size found is listed so you can see what was there.

Do cursor files work?

Yes. A CUR file uses the same container as an ICO and is read the same way.

Why does my icon look soft in the PDF?

Because icons are small. A thirty two pixel image printed at any useful size has very little detail to work with, so use the largest version the file contains.

What is the difference between the PNG and DIB versions inside?

Modern icons store the large sizes as PNG and the small ones as old style bitmaps. Both are handled, and the tool shows which each entry uses.

Related PDF tools and reference

Reference: the ICO container is documented as part of the Windows icon format.