How to Reduce PDF File Size (Below 100 KB, Free)

Text is tiny. A 20-page contract of pure text is often under 200 KB, because a PDF stores letters as characters, not pictures. The weight almost always comes from images: photos, screenshots, logos, and especially scanned pages, where every single page is a full-resolution photograph.

Three things inflate a PDF the most — high-resolution embedded images, pages scanned at 300–600 DPI, and duplicated or uncompressed fonts and metadata. A single phone photo dropped into a document can add several megabytes on its own.

Because images dominate the file, the fastest win is to re-encode them at a sensible quality and strip the waste. That is exactly what a PDF compressor does, so you can shrink the file without touching the layout or rebuilding the document.

PDF AutoPilot's compressor runs entirely in your browser — nothing is uploaded — and shows you the exact saving before you download. Here is the whole process:

Most bounced attachments come down to a handful of caps. Gmail and Google Workspace reject any message over 25 MB with attachments included; Outlook.com and Microsoft 365 default to around 20 MB; and many corporate mail servers are stricter still at 10 MB.

Web forms and government portals are far tighter. Job applications, court e-filing, and exam sites frequently cap a document at 1 MB, 500 KB, or even 100 KB per file. WhatsApp allows documents up to 100 MB, but the person receiving it may be on a mail service that does not.

The safe move is to compress to comfortably under the limit rather than right at it, because email adds roughly a third in encoding overhead when it packages an attachment.

Getting below a named target is mostly about matching the compression level to how image-heavy the file is. As a rough guide: a text document with a few images will drop under 1 MB at the Recommended level and often under 500 KB at Strong, while a scanned document usually needs Strong or Maximum to clear 500 KB.

Reaching below 100 KB is realistic for short, mostly-text PDFs — a one or two page letter, a resume without heavy graphics, a form. For a multi-page colour scan, 100 KB may not be possible without dropping pages or converting to grayscale first, because there is only so far image data can be squeezed before the text becomes unreadable.

If you overshoot on quality, compress again one level stronger; if the text starts to look soft, step back a level. The output size shown is the real encoded size, so you can dial it in without guessing.

Sometimes the fastest way under a limit is not to squeeze harder but to send less. If a portal caps each upload at 2 MB and your report is 8 MB across 40 pages, use Split PDF to break out only the section the form actually asks for, then compress that part.

The reverse is true when you have several files to send. Instead of attaching five separate PDFs, use Merge PDF to combine them into one document first, then compress the result once — a single optimised file is almost always smaller and tidier than five loose ones.

Whichever route you take, run the final file through the compressor last, so the saving applies to the finished document.