What is PDF?
Portable Document Format, created by Adobe Systems; ISO 32000 since 2008 in 1993.
PDF began as Adobe's answer to a problem that sounds quaint now and was genuinely hard then: a document created on one machine looked different, or failed to print, on another. Fonts were missing, printer drivers disagreed, and page geometry drifted. John Warnock's 1991 "Camelot" memo proposed capturing a finished document so completely that any machine could reproduce it exactly.
The result was a subset of PostScript with the programmability removed and a document structure added. That is why PDF pages are measured in PostScript points — 72 to the inch — and why a PDF describes shapes and glyphs rather than pixels.
Adobe handed the specification to ISO in 2008, and PDF has been an open standard since. The consequence for image work is that a PDF is a wrapper: it stores your image using an ordinary image codec, usually JPEG or a DEFLATE-compressed bitmap, plus instructions about where on the page it sits.
This matters more than it sounds. Converting an image to PDF does not re-compress it in any inherent way — what changes the file size is which codec goes inside the wrapper.
Technical specification
| Property | |
|---|---|
| Compression | Per-object: DCT (JPEG), Flate (PNG-style), JPX (JPEG 2000), CCITT for fax bitmaps |
| Bit depth | 1 to 16 bits per channel, depending on the embedded object |
| Transparency | Yes — soft masks, though most viewers composite onto white |
| Animation | No |
| HDR | No |
| Maximum dimensions | 14,400 × 14,400 points (200 × 200 inches) per page |
| Colour spaces | DeviceRGB, DeviceCMYK, DeviceGray, ICC-based, Separation, Indexed |
| Metadata | XMP document metadata; embedded image EXIF is generally discarded |
PDF support in browsers and operating systems
Checked on 2026-08-10. We re-verify this table every quarter.
| Platform | Support |
|---|---|
| Chrome | built-in viewer since 2010 |
| Safari | built-in, all versions |
| Firefox | built-in pdf.js viewer since Firefox 19 |
| Edge | built-in, default handler on Windows |
| iOS | Files, Mail, Safari and Books open PDFs natively |
| Android | Google Drive viewer preinstalled on most devices |
| Windows | Edge handles PDFs out of the box |
| macOS | Preview, all versions |
PDF compared with nearby formats
Against JPG. A JPG is an image; a PDF is a document that can contain one. For a single photograph headed somewhere on the web, JPG is smaller and displays inline. For anything that will be printed, signed, archived or attached to a form, PDF is what the recipient expects.
Against TIFF. Both handle multiple pages and both are used for scans. TIFF is the archival choice in libraries and imaging systems because it can be genuinely lossless and carries richer technical metadata. PDF wins on ubiquity — everyone can open one without installing anything.
Against PNG. PNG is the better choice for a screenshot that goes into a chat message or a web page. PDF is better when the screenshot is one page of something larger, or when it needs to print at a predictable size.
When to use PDF, and when not to
Convert to PDF when the destination is a document workflow: a form upload that demands PDF, an email attachment somebody will print, a scan to archive, or several images that belong together as one file.
Do not convert to PDF for the web. Browsers will usually download rather than display it inline, search engines index it poorly compared with a real page, and the file is larger than an equivalent WebP or AVIF.
Do not use PDF as an editing format. Extracting an image back out of a PDF gives you whatever was embedded, at whatever quality it was embedded — the original is gone. Keep the source file.
Frequently asked questions
Why is my image-to-PDF page a strange size?
Because PDF measures pages in points, at 72 points to the inch, and our converter sizes the page to match the image exactly. A 3000-pixel-wide image therefore becomes a 3000-point page. Nothing is cropped or stretched, and every viewer scales it to fit your screen or paper. The alternative — forcing A4 — would either crop the image or surround it with margins.
Is text in my PDF searchable after converting from an image?
No. The PDF contains a picture of the text, not the text itself, so nothing is selectable or searchable. Making it searchable requires OCR, which recognises the characters and adds an invisible text layer behind the image.
Why did my PDF come out smaller than the PNG I converted?
Because an opaque image is embedded as JPEG rather than stored losslessly. PDF supports JPEG natively and every viewer decodes it instantly, so a screenshot that was 1 MB as PNG often lands under half that. When the source has transparency the lossless path is used instead, and the sizes come out similar.
Can a PDF hold several images as separate pages?
Yes — that is one of the format's core features. Our converter does not build multi-page documents yet, so each image becomes its own single-page PDF. A proper builder with page ordering is planned rather than approximated.