Free tool · PDF · Runs in your browser
Convert PNG to PDF
Short answer
Choose PNG files and the tool puts each on a page of a PDF, in your browser with no upload. The PDF keeps every pixel: in our test the decoded picture inside the PDF matched ffmpeg's decode of the PNG exactly in 3 of 3 files we checked, including a transparent insignia.
Nothing is uploaded. JPEG and PNG files go into the PDF as they are; other formats are converted in your browser first.
Key takeaways
- Lossless: the pixels inside the PDF were identical to the PNG's pixels in 3 of 3 files compared (a screenshot, a portrait and a document scan).
- Size depends on the picture: 29.8 MB → 29.7 MB, 8.66 MB → 8.63 MB, 94.6 KB → 77.7 KB, 18.9 MB → 23.9 MB, 2.75 MB → 2.74 MB for the five PNGs we tried.
- Transparency costs space: the insignia with an alpha channel grew by 27% because the PDF stores the transparency as a second image (a soft mask).
- Large PNGs take seconds: the 29.8 MB photograph PNG took 4.1 s, the 94.6 KB screenshot 138 ms, because the PNG is decoded and written again.
- A PNG photograph makes a huge PDF: 29.7 MB for one picture. Convert photographs to JPG first if size matters.
Measured: PNG in, PDF out
Size depends on the picture: a 94.6 KB screenshot became 77.7 KB (-18%), a document scan PNG of 8.66 MB became 8.63 MB, and a transparent PNG of 18.9 MB became 23.9 MB (+27%).
Measured with the tool's own code (the same function the page runs) in headless Chromium on public domain NASA and National Archives pictures, a camera photo from Wikimedia Commons, and files we made from them. Each PDF was then opened by pdf.js, which reported its page count and page sizes, and by pdf-lib, which read back the picture streams: a JPEG in the PDF was compared byte for byte with the file you chose, and PNG pixels were compared with ffmpeg's decode.
| Picture | PNG | Change | Time | Pixels identical | |
|---|---|---|---|---|---|
| Photograph 3840 × 3877 PNG | 29.8 MB | 29.7 MB | -0.3% | 4.1 s | not checked |
| Document scan PNG | 8.66 MB | 8.63 MB | -0.3% | 1.8 s | Yes |
| Screenshot of a web page | 94.6 KB | 77.7 KB | -17.9% | 138 ms | Yes |
| Mission insignia with transparency | 18.9 MB | 23.9 MB | +26.8% | 4.7 s | not checked |
| Portrait 636 × 792 PNG | 2.75 MB | 2.74 MB | -0.3% | 375 ms | Yes |
A flat screenshot shrank because the PDF writer compresses the raw pixels with Deflate, the same algorithm as PNG (Wikipedia: PNG uses DEFLATE), with different settings; a transparent picture grew because its alpha channel becomes a separate image.
Measured: what a transparent PNG becomes inside the PDF
| Object in the PDF | Width × height | Filter | Color space | Bytes |
|---|---|---|---|---|
| Picture (with a mask) | 5380 × 5432 | FlateDecode | DeviceRGB | 23.8 MB |
| Mask | 5380 × 5432 | FlateDecode | DeviceGray | 85.3 KB |
Both objects are Flate (deflate) streams. The colors are stored without the transparency, and the transparency is stored as a grayscale image of the same size. A viewer combines them when it draws the page. That doubles the number of pixels the PDF stores, which is why the file grew while the flat screenshot shrank.
What the PDF holds
PDF stores the PNG's pixels as a Flate stream, which Wikipedia describes as a filter based on the deflate algorithm. The picture is stored as RGB with the alpha channel as a separate mask when the PNG has one. In our test the transparent insignia was stored as 2 image objects (5380 × 5432 DeviceRGB with a mask and 5380 × 5432 DeviceGray).
Page size: same as the picture, A4 or Letter
The tool offers three page sizes. "Same size as the picture" sets each page to the picture at 150 pixels per inch, so a 3840 pixel wide photo becomes a page 25.6 inches wide (1843.2 points; Wikipedia gives the PostScript point as 1/72 of an inch). A4 is 595.28 × 841.89 points, which Wikipedia lists as 210 mm × 297 mm, and US Letter is 612 × 792 points, or 8.5 × 11 inches. On A4 and Letter the picture is scaled to fit inside a 0.5 inch margin, centered, and the page turns to landscape for a picture wider than tall.
PNG or JPG inside the PDF?
This tool keeps a PNG lossless. For photographs that is large: the 3840 × 3877 photograph PNG made a PDF of 29.7 MB while the same photograph as a JPEG made one of 3.10 MB. For screenshots, diagrams and text scans the PNG is often the better choice; for photographs, convert to JPG first.
Free tools:Convert PNG to JPG firstJPG to PDFAny picture to PDFMerge PDF files
Questions people ask
How do I convert PNG to PDF?
Choose your PNG files above, set the order and page size, and download the PDF. It works in your browser.
Does it keep transparency?
Yes. A PNG with an alpha channel keeps it as a mask inside the PDF; the page behind is white in most viewers.
Does the quality change?
No. The pixels in the PDF matched the PNG's in 3 of 3 files we compared.
Why is my PDF bigger than the PNG?
A picture with transparency stores its alpha as a second image, and PNG photographs are already large. Our transparent test file grew +27%.
Why is my PDF smaller than the PNG?
Flat graphics such as screenshots can be compressed a bit further when written into the PDF. Ours shrank -18%.
Is my picture uploaded?
No.
Can I put PNG and JPG in the same PDF?
Yes. Mix any pictures; each gets a page.
What page size should I use?
The size of the picture for a plain container, A4 or Letter for printing.
How do I make a smaller PDF from PNG photographs?
Convert the PNG to JPG first, then use the JPG to PDF tool.
Related
Sources and how we checked
- Wikipedia: PDF (filters) (read 2026-10-10)
- Wikipedia: PNG (read 2026-10-10)
- Wikipedia: Point (typography) (read 2026-10-10)
- Wikipedia: ISO 216 (A4) (read 2026-10-10)
- PDF.js (Mozilla): the reader used to check every PDF (read 2026-10-10)
Reviewed October 10, 2026. The measurements ran the tool's own code and then opened every PDF with pdf.js and pdf-lib to compare pages, sizes, text and picture bytes. The files and results are in data/seo/hub/evidence/2026-10-10/pdf.