Last updated 24 September 2026
Government, university and job portals almost always test a file on the same four points: its size in bytes, its type, its dimensions in pixels if it is a picture, and sometimes its name. The error message rarely says which one failed — "invalid file" can mean any of them — so it pays to check all four before you try again.
A kilobyte can mean 1,000 bytes or 1,024 bytes, and both are in everyday use. A limit of "100 KB" is therefore either 100,000 bytes or 102,400 bytes, depending on how the portal was built — and it does not tell you which.
Your own computer adds to the confusion. Windows File Explorer counts in blocks of 1,024 but still writes "KB", while a Mac counts in thousands. A photo of 101,000 bytes appears in Windows as roughly 99 KB — under the limit on your screen, over it on a portal that counts in thousands.
The safe rule is to stay under the smaller number. When you type 100 KB into the compressors on this site, the target is 100,000 bytes, so the result passes whichever way the portal counts. If the portal says "maximum 100 KB", aim a few kilobytes lower rather than landing exactly on the line.
Renaming photo.heic to photo.jpg does not change the file. Many portals look at the first bytes of the file rather than its name, and they will reject it — or accept it and then fail to display it to the officer reviewing your application.
JPG and JPEG are the same format with two spellings; a portal that asks for one accepts the other. HEIC is different: it is the format iPhones use by default, and many portals and older Windows computers cannot read it. Convert it properly with HEIC to JPG, or change the iPhone setting for future photos under Settings › Camera › Formats › Most Compatible.
For documents, "PDF only" means a real PDF. A photo of a page saved as a JPG is not accepted in its place; JPG to PDF turns one or several photos into a single PDF.
Photo rules are often written in millimetres because they come from printed passport photos — 35 × 45 mm is the most common. An upload is measured in pixels. The bridge between the two is DPI (dots per inch): pixels = millimetres ÷ 25.4 × DPI. At 300 DPI, 35 × 45 mm is 413 × 531 pixels.
Changing the DPI number stored inside a file does nothing on its own: a picture that is 800 pixels wide stays 800 pixels wide. If a portal asks for a minimum or maximum pixel size, the picture itself has to be resized, and if it asks for a shape — square, or 35 by 45 — it has to be cropped to that shape rather than stretched, or the face comes out distorted and the photo is refused by a person even if the software lets it through.
For visa and passport photos, the visa photo maker carries the pixel, size and shape rules for each destination it lists, with the date each rule was last checked against the official source.
The order matters. Each step removes bytes without touching what the portal cares about, and the last one is the only one you can see:
A PDF made from a Word document is usually small, because its letters are stored as text. A PDF made by scanning or photographing paper is a set of pictures, and pictures are what make a PDF large.
For printed documents, 150 to 200 DPI is enough to read comfortably, and a black-and-white page does not need to be scanned in colour. If a portal gives you several upload boxes, one document per box is often easier to fit than everything combined. Compress PDF takes a target size, and Split PDF separates a long file into parts.
Signature boxes are usually the strictest of all — some Indian exam and bank portals ask for a JPG of 10 to 20 KB. Sign in dark ink on plain white paper, photograph it in daylight without a shadow, crop tightly around the signature, then shrink it. Resize signature does the last two steps to the size those portals ask for.
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