How to make a PDF smaller for email and upload forms

The form says “maximum 5 MB” and your PDF has 38. Before compressing anything, it helps to know what is making the file heavy.

Updated October 9, 2026 · 4 min read

Upload limits are everywhere: job applications, university portals, government services, insurance claims. Email has limits too — Gmail accepts attachments up to 25 MB per message, and Outlook usually 20 MB. When a PDF is over the limit, the right fix depends on why it is big in the first place.

What makes a PDF large

Text in a PDF is extremely light. A hundred pages of plain text can fit in well under a megabyte, because each letter is stored as a character plus a font, not as an image. Almost every oversized PDF is oversized because of images:

Scans. A scanner set to 600 DPI in color produces pages of several megabytes each. For a document you only need to read, that is far more than necessary.
Photos from a phone. A modern phone photo is 12 megapixels or more. Ten of them turned into a PDF can easily pass 30 MB.
Images pasted into Word or PowerPoint at full resolution, then exported to PDF.
Embedded fonts add some weight, but rarely enough to be the main problem.

Methods, from best to last resort

1. Fix it at the source

The cleanest result comes from making a lighter PDF to begin with. Rescan at 150–200 DPI — plenty for reading and printing — and in grayscale if color does not matter. In Word, choose Save as PDF and select the option to optimize for minimum size. For photos, resize them before turning them into a PDF; nobody needs 4000 pixels of width to read an ID card.

2. Split instead of compressing

If the limit is per file and the form accepts several files, splitting a long document into parts keeps full quality. Many portals also only want specific pages; sending pages 1–3 instead of the whole 40-page contract solves the problem without touching quality.

3. Compress by turning pages into images

When the source is not available, a browser-based compressor can render each page as an image at a lower resolution and rebuild the PDF from those images. This works very well on scans and photo-heavy documents, often cutting the size by 70–90%.

It has a real price, and you should know it before using it: the text stops being text. You can no longer select, copy or search it, and screen readers cannot read it. For a scan, nothing is lost, because the text was never text. For a PDF exported from Word, it is a bad trade — and often a useless one, because a page image is heavier than the text it replaces. A good tool will tell you when the “compressed” file came out larger and suggest keeping the original.

Choosing the settings

Resolution: around 110–150 DPI keeps documents readable on screen and in print. Go lower only if the limit forces you to, and check the smallest text afterwards.
Image quality: 70% is a good balance for documents. Below 50%, text edges start to blur.
Check the result at 100% zoom on the page with the smallest print — usually the signature line or footnotes.

Privacy: think about what you are compressing

The documents people need to shrink are rarely holiday photos. They are pay slips, medical reports, contracts and identity documents — exactly the files you should not upload to an unknown service. A compressor that runs in your browser processes the file on your device: you can confirm it in the Network tab of your browser’s developer tools, where no request carries the document.

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Frequently asked questions

Why did my compressed PDF get bigger?

Because it was mostly text. Text is stored as characters, which take almost no space; turning a page of text into an image always makes it heavier. In that case keep the original, or split the document instead.

Will compression affect a digital signature?

Yes. Any change to a signed PDF invalidates the signature. Compress the document before signing it, never after.

What resolution is enough for a scanned document?

For reading and ordinary printing, 150 DPI is enough; 200 DPI gives a margin for small print. 300 DPI and above matters only for photos or archival copies.

Can I still search the text after compressing?

Not when compression turns pages into images. If searchable text matters, fix the size at the source instead — rescan at a lower resolution or export again with a smaller-size option.