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Convert PNG to PDF Online Free — Fast Batch Conversion
How to Convert Images Online
1Upload PNGs
Drag and drop one or more PNG files. Transparency detected automatically.
2Choose settings
Select page size (A4, Letter, Fit-to-Image), margins, and page orientation.
3Download PDF
Click Convert. Download your PDF with transparency preserved. Files deleted immediately.
Supported Image Formats
PNG
Lossless format that preserves every pixel. Best for screenshots and logos.
PDF
Portable Document Format. Convert PDF pages to JPG, PNG or WebP images.
HEIC
Apple photo format used by iPhone and iPad. High quality with small file size.
HEIF
High Efficiency Image Format — same as HEIC, used on Apple devices.
WebP
Modern image format by Google. Up to 30% smaller than JPG with the same quality.
JPG
Universal format for photos. Supported everywhere, great balance between quality and file size.
GIF
Classic format for simple animations. Supports transparency and up to 256 colors.
BMP
Uncompressed bitmap format. Maximum quality but very large file size.
TIFF
Professional lossless format used in printing and photography.
AVIF
Next-gen format with excellent compression. Up to 50% smaller than JPG.
PPM
Portable Pixmap format used in Unix/Linux environments.
HDR
High Dynamic Range format storing extended brightness data.
FITS
Flexible Image Transport System used in astronomy and science.
AVIF vs WebP vs HEIC vs JPG
Quick comparison to help you choose the right format
AVIF
- Size: Up to 50% smaller than JPG
- Browsers: Chrome, Firefox, Safari
- Transparency: ✓
- Best for: Web performance
WebP
- Size: 25-35% smaller than JPG
- Browsers: All modern browsers
- Transparency: ✓
- Best for: Web compatibility
HEIC
- Size: ~50% smaller than JPG
- Browsers: Safari only
- Transparency: ✓
- Best for: iPhone storage
JPG
- Size: Baseline
- Browsers: All browsers & apps
- Transparency: ✗
- Best for: Universal sharing
Frequently Asked Questions
- Does PNG to PDF preserve transparency?
- Yes. Convertify writes proper SMask soft masks that preserve full 8-bit alpha. The transparency appears white in PDF viewers because they paint white page backgrounds, but the alpha data is intact.
- Why is my PNG-to-PDF file so large?
- PDF uses FlateDecode — the same lossless compression as PNG itself. A 5 MB PNG produces a ~5 MB PDF. This is the honest cost of zero quality loss.
- Can I combine multiple PNGs into one PDF?
- Yes. Upload multiple PNGs — each becomes a page. Upload order determines page order.
- Does conversion lose quality?
- No. FlateDecode preserves every pixel losslessly. The output is pixel-identical to the input.
- Can I fit PNGs to A4 or Letter?
- Yes. Choose A4, Letter, Legal, or Fit-to-Image (page matches PNG dimensions exactly).
- My Mac screenshots produce blurry or oversized pages — why?
- Retina screenshots are saved at 144 DPI. Convertify fits to page automatically, but you can also fix with: sips -s dpiHeight 72 -s dpiWidth 72 screenshot.png.
- Can I place a transparent PNG signature on a PDF?
- Yes — if the converter preserves SMask. Convertify does. Use Acrobat Edit PDF → Add Image for placement.
- Which PDF/A version supports transparency?
- PDF/A-2b and PDF/A-3b permit transparency via SMask. PDF/A-1b requires flattening to opaque.
- PNG or JPG — which should I use for PDF?
- PNG for screenshots, diagrams, logos, and anything with transparency. JPG for photographs — DCTDecode wrapping is more size-efficient.
- Does Convertify delete my files?
- Yes. Files are deleted immediately after download. Nothing is stored.
Transparency in PDF — how SMask preserves your alpha channel
PNG supports a full 8-bit alpha channel: 256 levels of opacity per pixel, from fully transparent through semi-transparent to fully opaque. The PDF specification (version 1.4 and later) preserves this through SMask — a soft mask that is stored as a separate single-channel grayscale image alongside the base RGB image. Each grayscale value maps directly to opacity. This means a PNG logo with a feathered drop shadow on a transparent background can be placed in a PDF and composited over any background — colored stationery, another image, or printed on colored stock — and the transparency blends correctly. Not all converters implement SMask. Cheap tools flatten the alpha channel against white, destroying the transparency permanently. Convertify writes proper SMask XObjects so your transparency survives the conversion intact.
The white-background paradox — your transparency IS preserved
The most common complaint about PNG-to-PDF conversion is that the transparent background became white. In most cases the transparency is actually preserved correctly — the problem is how PDF readers display it. Acrobat, Preview, Chrome, and every other PDF viewer paints a white page background before drawing content. Your transparent PNG is composited over this white background, making it appear as though the transparency was lost. Open the PDF in Illustrator or InDesign, place it over a colored rectangle, and you will see the transparency working. This is not a bug in the converter — it is how PDF rendering works. If you genuinely need to see transparency in a PDF viewer, some tools support configuring the page background, but for practical purposes the transparency is there and will work correctly when the PDF is used downstream in print or design.
Why your PNG-to-PDF file is so large — lossless means lossless
PDF embeds PNG data using FlateDecode with Predictor 15 (PNG-Up or Paeth prediction filter) — this is the exact same DEFLATE compression that PNG uses internally. The result: a 5 MB PNG becomes a roughly 5 MB PDF stream. Twenty 3 MB Mac Retina screenshots produce a 60 MB PDF. This is not a bug, it is lossless preservation. The pixel data is stored without any quality degradation. If file size matters more than pixel-perfect preservation — for email attachments or portal uploads — consider re-encoding photographic PNGs as JPG before conversion. For line art, diagrams, and UI screenshots, the lossless path is correct and the large file size is the honest cost of zero quality loss.
Page size, DPI math, and the Mac Retina screenshot trap
PDF pages are measured in points (1 point = 1/72 inch). A4 is 595 × 842 points, Letter is 612 × 792 points. When you place a PNG on a PDF page, the converter calculates the physical size using the PNG DPI metadata. A 1920 × 1080 PNG at 72 DPI would fill 26.67 × 15 inches — far larger than A4. At 150 DPI the same PNG fills 12.8 × 7.2 inches — closer but still overflows. The Retina trap: Mac screenshots on Retina displays are saved at 144 DPI (2× the standard 72). A 2880 × 1800 screenshot at 144 DPI calculates to 20 × 12.5 inches — which overflows A4 and produces a page that looks blurry when scaled down to fit. The fix on Mac is to strip the 144 DPI metadata with sips: sips -s dpiHeight 72 -s dpiWidth 72 screenshot.png. Convertify applies fit-to-page scaling automatically regardless of embedded DPI metadata, so this trap does not affect the output.
Use cases — who converts PNG to PDF and why
UI/UX designers combining Figma or Sketch 2× exports into client presentation PDFs. Frontend developers assembling Lucidchart or draw.io architecture diagrams into specification documents. QA engineers filing bug reports with annotated Mac screenshots — the PDF bundles evidence into a single shareable file. Legal and HR teams placing transparent PNG signatures onto company letterhead PDFs. Pixel artists and illustrators building portfolio PDFs where each page is one artwork with zero margins. Architects combining high-resolution floor plan renders into tabloid-size specification books. Manga and webcomic creators assembling transparent-bordered panels into A5 or B5 book PDFs for print submission.
PNG vs JPG vs WebP for PDF embedding
| Feature | PNG → PDF | JPG → PDF | WebP → PDF |
|---|---|---|---|
| PDF filter | FlateDecode (lossless) | DCTDecode (lossless wrap) | Transcode to DCT or Flate |
| Quality | Pixel-perfect | Pixel-perfect (no re-encode) | Minimal loss on transcode |
| Transparency | Yes — SMask 8-bit alpha | No — JPG has no alpha | Yes if FlateDecode path |
| File size | Large (same as source PNG) | Small (same as source JPG) | 1.5–5× larger than source WebP |
| Best for | Screenshots, diagrams, logos, design | Photos, receipts, scans | AI images, web downloads |
PDF/A archival — which version allows transparency
PDF/A-1b (2005) forbids transparency entirely — all alpha must be flattened to an opaque background. If your archival system requires PDF/A-1b, your transparent PNGs will be composited against white. PDF/A-2b (2011) and PDF/A-3b (2012) permit transparency via SMask — use these if you need archival compliance with preserved alpha. PDF/A-3b additionally allows embedding the original PNG files as associated files inside the PDF — true archival where both the rendered page and the source assets are preserved in one container.
Troubleshooting common PNG to PDF problems
Transparent background appears white: likely not a bug — PDF viewers paint white backgrounds. Check by placing the PDF over a colored layer in Illustrator. If transparency is genuinely lost, the converter flattened alpha instead of writing SMask. PDF file is huge: expected — FlateDecode preserves lossless PNG data. Twenty 3 MB screenshots = 60 MB PDF. Compress only if you accept quality loss. Mac screenshots produce oversized or blurry pages: 144 DPI Retina metadata causes scaling issues — Convertify fits to page automatically. Multi-PNG pages in wrong order: alphabetical sort makes screenshot10.png precede screenshot2.png — rename with zero-padded numbers. PNG signature appears pixelated in Acrobat: Fill and Sign downsamples — use Edit PDF → Add Image instead. Signature prints as a black box: 8-bit alpha bug in some PDF printers — convert to 24-bit with white matte before embedding. Colors look washed out: embedded ICC profile not sRGB — strip non-sRGB profiles before conversion.