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How to Convert PNG to PDF on Mac, Windows, and Linux

You have a PNG screenshot, a scanned document, or a batch of images that need to become a PDF. Here's how to do it locally, with full control over page size, resolution, and compression.

Why convert PNG to PDF?

PNG is an image format. It holds pixels. PDF is a document format. It holds pages. The distinction matters because the world runs on PDFs for anything that needs to be shared, printed, signed, or archived.

Sending a PNG to someone who expects a document creates friction. They cannot annotate it in Adobe Acrobat. They cannot sign it with DocuSign. They cannot combine it with other pages. They cannot print it at a predictable size because PNG carries no page dimension information.

Converting PNG to PDF solves all of these problems. The image gets placed on a page with defined dimensions (A4, Letter, or custom). It becomes a document that fits into every workflow that expects PDF input. The PNG specification was designed for lossless image storage and web display, not for document exchange. PDF fills that gap.

Common scenarios where you need PNG-to-PDF conversion:

• Scanned receipts and documents: Your scanner or phone camera produces PNG (or JPEG) images. Submitting them for expense reports, insurance claims, or legal filings requires PDF.
• Screenshots for documentation: You are writing a user manual and need to compile screenshots into a single document.
• Design proofs: Your designer exports PNG mockups. The client wants a single PDF to review and annotate.
• Forms and signatures: You photographed a signed document. The recipient needs it as a PDF to file.
• Archival: The PDF/A standard is an ISO-recognized format for long-term document archival. PNG is not.

PNG vs PDF: understanding the formats

These are fundamentally different types of files. Understanding what each does helps you make better decisions about resolution, compression, and page layout during conversion.

The key takeaway: PNG stores an image. PDF stores a document that can contain images. When you convert PNG to PDF, the image data gets embedded inside a PDF page structure. The pixels do not change (unless you apply compression). For the full PDF specification and its capabilities, refer to the PDF article on Wikipedia.

Single image to PDF

convx convert photo.png --to pdf

This is the simplest case. ConvX takes the PNG, places it on a page sized to match the image dimensions at 150 DPI, and writes a PDF. The image quality is preserved because the PNG data is embedded without lossy recompression. The output file is ready to share, print, or upload to any system that expects PDF. Check the full set of flags in the CLI reference.

Batch convert multiple PNGs to individual PDFs

convx convert *.png --to pdf

Every PNG in the current directory becomes its own PDF file. If you have 50 scanned receipts as PNGs, this gives you 50 individual PDF files. ConvX processes them in parallel by default, so even large batches finish quickly.

Combine multiple PNGs into a single multi-page PDF

convx convert *.png --to pdf --merge

This is what you want when compiling a document from multiple images. Each PNG becomes one page in the output PDF. Pages appear in alphabetical filename order. If your files are named page-01.png, page-02.png, page-03.png, they will appear in the correct order.

This is the command you need for scanned multi-page documents, photo albums, design proof decks, and any situation where a stack of images should become a single document.

Resolution and DPI explained

DPI (dots per inch) determines how the pixel dimensions of your PNG translate into physical page dimensions. This is the most misunderstood aspect of image-to-PDF conversion.

A 3000x2000 pixel PNG at different DPI settings produces different page sizes:

For most use cases, 150 DPI is a good default. It produces readable documents at a reasonable page size. For print-quality output (submitting to a printer or publisher), use 300 DPI. ConvX defaults to 150 DPI but you can override it.

If you want the page to match a standard paper size instead of calculating DPI yourself, use the page size flag:

convx convert scan.png --to pdf --page-size a4

This scales the image to fit on an A4 page (210 x 297 mm) while preserving the aspect ratio.

Compression options

PNG files are already losslessly compressed using DEFLATE. When embedding a PNG into a PDF, you have three choices for how the image data is stored inside the PDF.

Lossless (default): The PNG pixel data is stored in the PDF using lossless compression. File size is similar to the original PNG. Use this when quality matters more than size: legal documents, medical images, technical diagrams.

JPEG compression: The image data is recompressed using JPEG inside the PDF. This can reduce file size by 60 to 80% compared to lossless, but introduces compression artifacts. Good for photographs and scanned documents where exact pixel accuracy is not required.

convx convert photo.png --to pdf -q 80

Quality 80 produces a PDF that is significantly smaller with minimal visible artifacts. Quality 60 works for documents that will only be viewed on screen. Below 50, text in screenshots starts to look blurry.

Downsampling: If the source PNG is much higher resolution than needed, you can reduce the image dimensions before embedding. A 6000x4000 pixel photo does not need full resolution for a Letter-size PDF viewed on screen.

convx convert photo.png --to pdf --width 2400

This resizes the image to 2400 pixels wide (maintaining aspect ratio) before placing it in the PDF. At 300 DPI, that gives you an 8-inch-wide image on the page, which is more than sufficient for Letter-size paper.

Platform-specific instructions

Mac

macOS has built-in PNG-to-PDF support through Preview. Open the PNG in Preview, go to File, then Export as PDF. For a single image, this works fine. The limitation: you cannot control DPI, compression, or page margins. For multi-page PDFs, you can select multiple files in Finder, right-click, and choose Quick Actions, then Create PDF. But the page ordering is unreliable, and you cannot adjust quality settings.

The Automator app can create a workflow for batch conversion, but it is slow and offers no compression control. For anything beyond the simplest use case, ConvX gives you full control from the terminal or the desktop app.

Windows

Windows 10 and 11 include a "Microsoft Print to PDF" printer. Open the PNG in Photos, click Print, select "Microsoft Print to PDF," and save. This works for single images but is tedious for batches. You cannot control image quality, DPI, or page size. The "print" metaphor also means the image goes through a rendering pipeline that may change its appearance.

For batch conversion, there is no built-in Windows tool. PowerShell scripts exist but require installing additional libraries. ConvX handles batch PNG-to-PDF natively on Windows with a single command.

Linux

Linux users have several command-line options. ImageMagick's convert command can do it: convert image.png output.pdf. However, ImageMagick has known security issues with PDF handling (the infamous ImageMagick policy.xml restrictions), and its PDF output quality varies. LibreOffice can also convert images to PDF via the command line, but it is heavyweight (requires the full office suite installed).

ConvX on Linux uses purpose-built PDF generation that avoids these issues. It runs without dependencies beyond what ships with the AppImage.

Handling transparency

PNG supports alpha channel transparency. PDF also supports transparency. But when converting PNG to PDF, transparency behavior depends on how the PDF will be used.

If the PDF will be viewed on screen, transparency is preserved. The image appears with a transparent background in PDF viewers that support it (which is most modern viewers).

If the PDF will be printed, transparent areas need a background. Most printers treat transparency as white, but results vary. For reliable printing, flatten the transparency to a white background before conversion:

convx convert transparent-logo.png --to pdf --bg white

If you are sending a PDF with a transparent PNG to someone for review, add a note that they should check background rendering in their viewer. Some older PDF readers (especially on Windows) render transparency as black instead of white.

Scanned documents: getting the best results

Phone cameras and flatbed scanners produce PNG or JPEG images of physical documents. Converting these to PDF has specific considerations.

Alignment: Photos taken at an angle produce skewed text. While ConvX does not perform deskewing (that requires OCR software), you can crop and rotate images before conversion.

Resolution: A typical phone camera produces images at 4000x3000 pixels or higher. For a scanned letter-size document, this is overkill. Downsampling to 2550x3300 pixels (300 DPI at Letter size) reduces file size without losing legibility.

Color vs grayscale: Text documents scanned in color produce files 3 to 4 times larger than grayscale. If the document is just black text on white paper, converting to grayscale before PDF conversion saves significant space.

Multi-page scans: If you scanned a 20-page document and have 20 PNG files, combine them into a single PDF:

convx convert "scan-*.png" --to pdf --merge -q 75

Quality 75 with JPEG compression inside the PDF produces a compact document that is still perfectly readable. A 20-page scanned document that would be 60 MB as raw PNGs becomes 3 to 5 MB as a compressed PDF.

Using the desktop app

Drag one or more PNG files into ConvX. Select PDF as the output format. The app shows a preview of the first page. For multi-file drops, toggle "Merge into single PDF" to combine all images into one document. The quality slider controls compression. The page size dropdown lets you choose A4, Letter, or auto-fit. Click convert.

The desktop app is the fastest path for occasional conversions where you do not want to open a terminal.

AI-powered conversion via MCP

You: "Convert all the screenshots in my Desktop folder to a single PDF"

Claude (via MCP): batch_convert({
  input_paths: ["~/Desktop/*.png"],
  output_format: "pdf",
  merge: true,
  quality: 85
})

ConvX's MCP server lets AI assistants handle file conversion through natural language. Describe what you want, and the AI calls the right ConvX function with the right parameters. No command memorization needed.

Troubleshooting

PDF file is much larger than the original PNG

This happens when the PNG is small (a simple icon or diagram with few colors) and the PDF embeds it without compression. PNG's DEFLATE compression is very efficient for images with large areas of uniform color. The PDF's internal storage may use a different compression method that is less efficient for this type of image. The fix: use quality-based compression to enable JPEG encoding inside the PDF.

convx convert diagram.png --to pdf -q 90

Quality 90 preserves visual fidelity while using more efficient compression for the PDF's internal image storage.

Image appears cropped or misaligned in the PDF

This typically occurs when the PDF page size does not match the image aspect ratio. If you specify --page-size a4 and the image is landscape while A4 is portrait, the image gets scaled to fit within the portrait page, leaving white bars. Swap to landscape:

convx convert screenshot.png --to pdf --page-size a4-landscape

Or let ConvX auto-detect the orientation by omitting the page size flag entirely. It will choose portrait or landscape based on the image dimensions.

Colors look different in the PDF

PNG files can embed ICC color profiles (sRGB, Adobe RGB, Display P3). PDF viewers may interpret these profiles differently from image viewers. The most reliable approach is to convert the color profile to sRGB before embedding, which ConvX does by default. If your PNG uses a wide-gamut profile and you need to preserve it, check your PDF viewer's color management settings before assuming the conversion is at fault.

Text in screenshots is blurry in the PDF

This happens when JPEG compression is too aggressive on images containing text. Text has sharp edges that JPEG compression smears. For screenshots with text, use quality 85 or higher. For documents that are primarily text, quality 90 is recommended. If file size is not a concern, omit the quality flag entirely to use lossless embedding.

Related articles

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• How to Batch Convert Files from the Command Line