Why Upload Portals Cap PDFs at 100KB (and How to Actually Hit It)

You have filled in the form, scanned the documents, and reached the last step. The upload box rejects your file: maximum size 100KB. Your scan is 3.4MB.

This is one of the most frustrating parts of any official application, and the advice you find is usually wrong — "just save it smaller" is not a setting that exists. This guide explains why these caps are set so low, and how to get a genuine document under one without turning it into a grey smudge.

Why the Limits Are So Small

The caps look arbitrary. They are not — they usually come from one of four places.

Old systems that were sized for old documents. Many government and university portals were specified in the 2000s, when a scanned page was expected to be a 50KB fax-quality TIFF. The limit was generous then. The form has been re-skinned several times since; the number underneath has not moved.

Per-record storage budgets. An immigration department processing millions of applications a year, each with eight attachments, is planning storage in petabytes. A 100KB cap instead of a 1MB cap is a tenfold difference in a very large number.

Database column limits. Some systems store attachments as binary blobs in a database rather than as files. The column has a fixed maximum, and the upload limit is set just under it.

Deliberate friction. A small number of portals use size limits to discourage people from uploading entire scanned folders when one page was requested.

Knowing which one you are facing does not change what you have to do, but it does explain why the limit will not be raised if you ask.

What Actually Takes Up the Space

Before you compress anything, it helps to know what you are compressing. In a document you scanned or photographed, effectively all of the file is image data. The text you can see is not text as far as the file is concerned — it is a picture of text.

That matters because it determines how much you can save:

• A scanned or photographed page is mostly image data and will usually shrink by 60–80%.
• A PDF exported from Word or a web form is mostly real text and will only shrink by 20–30%, because there is very little image data to remove.

If your file came out of a scanner at 3.4MB, you are in the first case, and 100KB is achievable. If it came out of Word at 180KB and the cap is 100KB, you are in the second case, and you have far less room to work with.

The Three Things That Reduce Size

Only three levers matter, and every tool is some combination of them.

Resolution

How many pixels the page is stored at. A page scanned at 300 DPI holds roughly four times the data of the same page at 150 DPI. For a document a human will read on screen, 150 DPI is usually indistinguishable. For a document that will be printed or read by an automated checker, do not go below 150.

Image quality

How aggressively the image data is encoded. This is where the visible damage happens first — text edges go soft, then blocky. Small reductions here are nearly free; large ones are obvious.

Colour

A black-and-white document scanned in colour carries three channels of data for something that only needs one. Converting to greyscale often removes a third of the file on its own, with no visible change to a document that had no colour in it.

How to Hit a Specific Number

Guessing at a quality slider and re-checking the file size is the slow way to do this. It is also how people end up with an unreadable document — you overshoot, the file is 40KB, and you upload it because it fits.

Our Compress PDF tool has a Target size mode for exactly this. You type the size the portal demands, and the tool works backwards: it tests sample pages, searches for the quality level that lands under your number, then runs the full document at that setting. You get the largest, most readable version of your file that still fits.

There are dedicated pages for the caps that come up most often — 100KB, 200KB, 500KB and 1MB — which open the tool already set to that target.

One honest limitation: if you ask for 100KB from a 60-page colour scan, no tool can give you a readable result. The tool will tell you when your target is not reachable rather than silently returning something unusable.

What You Lose, and When It Matters

Every method that gets a scan under 100KB works by turning the pages into compressed images. That has one consequence worth knowing before you upload: the text in the output is no longer selectable or searchable.

For most portal uploads this is irrelevant. A human opens your file, reads it, and approves it. But check first if:

• The portal says it runs automated text checks on submissions
• You are submitting to a system that extracts data from the document
• You need to search the file yourself later

If any of those apply, use the Keep text mode instead. It rebuilds the file structure without touching the page content, so the text stays real. The saving is much smaller — often only 20–30% — but nothing is degraded.

Practical Order of Operations

1. Remove pages you were not asked for. The cheapest compression is not including the page. A five-page bank statement where only page one was requested is an 80% saving before you start.
2. Convert to greyscale if the document has no meaningful colour.
3. Set the target size to the portal's limit, not below it. There is no prize for coming in at 40KB.
4. Open the result and read it at the zoom level a reviewer would use. If a reference number is ambiguous, you have gone too far.
5. Keep the original. If the submission is queried, you will need the full-quality version.

When You Genuinely Cannot Get There

Occasionally the cap and the document are incompatible — a 40-page certified translation cannot become 100KB and remain legible. In that case:

• Check whether the portal accepts multiple attachments. Splitting a long document across the allowed slots is usually permitted, and our Split PDF tool will do it by page range.
• Check whether the limit is per file or per application. These are often different numbers.
• Submit the largest legible version and note the issue in any free-text field. A reviewer would rather have a readable document with a comment than an unreadable one that met the limit.

The goal is a file someone can actually read, that happens to fit. Not a file that fits, that happens to be a document.

Frequently Asked Questions

Why does the portal reject my file even though it is under the limit? Some systems apply the limit per application rather than per file, or count the encoded size rather than the size on disk. Try a slightly smaller target before assuming something is broken.

Can I ask for the limit to be raised? Almost never. These caps are usually set in the system's configuration or its database schema, not by the team reviewing your application.

Is it safe to compress official documents? The content is unchanged — compression affects how the pages are stored, not what they say. Keep the original in case the submission is queried.

Why can I not get my file under the limit? If the document is long, in colour, or already text-based, there may be no setting that reaches your target while staying readable. Reduce the page count first, then compress.

Will compressing make my document unreadable to the reviewer? Not if you target the limit rather than going as small as possible. Open the result and read it at normal zoom before submitting.

Does the file need to stay searchable? Usually not, but check whether the portal runs automated checks on submissions. If it does, use a lossless mode so the text layer survives.