Image to PDF

A PDF turns a folder of loose files into one document with a fixed order and a predictable appearance. That matters whenever something is being submitted rather than simply shared: application forms, expense claims, insurance documentation, school assignments and legal paperwork are almost always expected as a single PDF, and a ZIP of JPGs is frequently rejected outright.

It also solves an ordering problem. Images sent as separate attachments arrive in whatever sequence the mail client feels like, and file managers sort 'IMG_10' before 'IMG_2'. A PDF fixes the sequence permanently, so the person at the other end reads the pages in the order you intended.

Finally, a PDF prints predictably. Page size, orientation and margins are decided when the document is built rather than negotiated by whatever printer dialog the recipient happens to open.

A4 is the standard almost everywhere outside North America; Letter is slightly wider and shorter and is the US default. Choosing the one your recipient's printer expects avoids the scaling and clipping that happens when a Letter document meets an A4 tray.

'Fit to image' sizes each page to the picture instead, which is the right choice for screen-only documents, photo collections and anything with mixed orientations. It eliminates the bands of white space you get when a wide photo is centred on a tall page. Auto orientation is the middle ground: it keeps a standard sheet size but turns each page to match its image, so landscape photos stop being letterboxed.

The fit mode decides what happens when the image and the page still disagree. Contain shows everything and accepts the empty margins; Cover fills the sheet edge to edge and crops the overflow, which suits full-bleed photo pages; Stretch forces an exact fit and should be reserved for images whose proportions are already close, since it visibly distorts anything else.

Placing several images per page turns the same tool into a contact sheet or a handout. 2-up splits along the page's long edge, while 4, 6 and 9 lay out a reading-order grid — and the margin becomes the gutter between cells as well as the border around them.

The PDF is roughly as large as the images you put into it — they are embedded as they are, without recompression — so a document built from twenty 12-megapixel phone photos will run to tens of megabytes, usually well past the attachment limit of the system you are submitting to.

The fix is upstream. Resize the images to around 1500–2000 pixels on the long edge, which is more than enough for both screen reading and ordinary printing, and compress them before building. For photographed text documents, converting to grayscale first often halves the size again with no loss of legibility.

The PDF is assembled on your own device using a JavaScript PDF library, so the images are never uploaded. That is worth knowing given what people typically convert here — passports, bank statements, medical forms, contracts and ID documents are exactly the kind of thing that should not be passing through someone else's server.

A practical consequence is that the tool works offline once the page has loaded, and that very large batches are limited by your device's memory rather than by an upload cap.