Image to PDF: How It Works
Converting images to PDF bundles them into one document that opens identically everywhere, preserves order, and is accepted by systems that reject loose image files. It is the standard way to submit scanned documents, receipts and photographed paperwork.
Why a PDF rather than the images
- One file. Twelve receipt photographs become one attachment in the right order.
- Fixed layout. A PDF renders the same on every device and printer.
- Accepted everywhere. Government forms, insurance claims, university submissions and expense systems commonly require PDF and reject images.
- Printable as intended. Page size and margins are defined rather than left to whatever the viewer decides.
Page size and orientation
| Size | Dimensions | Used in |
|---|---|---|
| A4 | 210 × 297 mm | Most of the world |
| US Letter | 216 × 279 mm | North America |
| A5 | 148 × 210 mm | Booklets, receipts |
| Fit to image | Matches each image | Screenshots, mixed sizes |
Choosing the wrong standard is a common annoyance: an A4 document printed on Letter, or the reverse, either crops the edges or leaves an uneven margin. Match the destination's convention rather than your own default.
Set orientation per image where possible. Forcing landscape photographs into portrait pages wastes most of the page and shrinks the content.
Resolution and readability
| Purpose | Effective DPI |
|---|---|
| Screen viewing only | 150 |
| Text documents to be read or printed | 200–300 |
| Archival scanning | 300–600 |
| Photographs for print | 300 |
Below about 200 DPI, small print in a scanned document becomes hard to read and impossible for OCR. Above 400 DPI the file grows substantially with no practical gain for ordinary documents.
File size
PDFs of photographs get large quickly. Ten phone photographs at full resolution easily exceed 40 MB, and many upload forms cap at 5 or 10 MB. Three things control this:
- Resize images to the resolution actually needed before converting.
- Use JPEG compression inside the PDF rather than lossless.
- Convert scanned text to greyscale, which reduces size substantially with no loss of legibility.
What this does not produce
The result is a PDF containing images, so the text inside them is not searchable, selectable or accessible to a screen reader. Making it so requires OCR, which recognises the characters and adds an invisible text layer. If a document must be searchable — a contract, a reference record, anything you will need to find later — run OCR after converting.
Order and orientation
Check the page order before submitting. Files sorted by name put 'page10' before 'page2', which is the most common cause of a jumbled submission. Also confirm rotation: photographs taken in portrait sometimes carry an EXIF rotation flag that some converters ignore, producing sideways pages.
Conversion runs entirely in your browser, so documents containing personal or financial information are not uploaded anywhere.