BMP to PDF
Turn bulky BMP scans and bitmaps into a far smaller PDF.
or drop files anywhere on this page
Your files stay in this browser. Nothing is uploaded.
About BMP to PDF
BMP to PDF turns Windows bitmaps into a PDF you can email, archive or print. Files like these still come out of older scanners, Paint, lab and factory equipment, and software that has not changed in twenty years. Each BMP becomes a page, and the PDF is made in this browser tab.
A typical BMP stores every pixel with no compression at all, which is why a single scanned page can weigh several megabytes. The PDF keeps the same pixels but packs them, so the result is usually a fraction of the size with nothing lost.
How it works
- Select the BMP files, or drop them onto this page. A whole folder of scans can go in at once.
- Drag the page thumbnails into reading order, or use the Move button on one to type its position; scanners often number files in a way that sorts badly.
- Match the page size to the paper that was scanned, Letter or A4, so each scan fills its page.
- Convert, and download one PDF with every page, or clear "Merge into one document" for a PDF per file.
- If the pages are text, run the PDF through OCR PDF afterwards to make the words searchable.
Why the PDF is so much smaller
An everyday 24-bit BMP spends three bytes on every pixel, so its size depends only on its dimensions, never on what the picture shows. The PDF stores the same pixels with lossless compression, which squeezes hardest on plain backgrounds and large even areas:
- A letter page scanned at 150 dpi, 1275 by 1650 pixels, was 6.3 MB as a BMP and 163 KB as a PDF, about 39 times smaller.
- A 4032 by 3024 landscape picture was 36.6 MB as a BMP and 7.3 MB as a PDF, 5 times smaller. Busy photographs leave the compressor less to work with.
Choosing the page size for scans
A BMP does not reliably say what size of paper it came from, so the page size you pick decides how the scan is laid out. That 150 dpi letter scan fills a Letter page edge to edge. On the default A4 page it is scaled to the page width and leaves a thin white band above and below, because A4 is a little taller and narrower.
Fit to image is usually the wrong choice for a scan. It counts one pixel as one point, which assumes 72 dpi, so the same 150 dpi scan becomes a page 17.7 by 22.9 inches, more than twice the size of the sheet that went through the scanner.
After converting: searchable text and big batches
The pages of a scanned document are still pictures of text once they are in a PDF. OCR PDF reads them and adds a hidden text layer, so you can search, select and copy the words without changing how the pages look.
Every BMP is held in memory while the PDF is built, and they are large: forty photo-sized bitmaps would be over a gigabyte. On a phone or an older laptop, convert them in groups and join the PDFs with Merge PDF.
Frequently asked questions
A BMP normally stores pixels with no compression, while the PDF compresses them without loss. A scanned page went from 6.3 MB to 163 KB, and a large photo from 36.6 MB to 7.3 MB.
No. Every pixel of the bitmap is kept exactly; only the way it is packed changes. The picture is not sharpened, cleaned up or recoloured either.
The size of the original paper: Letter for US documents, A4 for most others. A scan then fills its page. Fit to image treats the scan as 72 dpi and makes an oversized page.
Not yet, since the page is still a picture. Run the PDF through OCR PDF, which recognises the words and adds a searchable text layer behind each page.
Yes. Add all the files, check the order of the thumbnails, and keep "Merge into one document" ticked. Each bitmap becomes one page of the same PDF.
The browser decodes the bitmap, and a few unusual BMP variants are beyond it. The conversion stops and names the file; open it in an image viewer and save it as PNG, then add that.
The tool sets none, but each bitmap is held in memory while the PDF is made. If a large batch stalls, convert it in smaller groups and join the results with Merge PDF.
No. They are decoded, compressed and written into the PDF by code running in this tab, which matters for scans of letters, records and ID documents.
Other formats
Related tools
This tool ran entirely in your browser and nothing was uploaded. Your Recent files list keeps a copy of local files under 5 MB until you clear it. How your files are handled.