How to Shrink a PDF Without Ruining the Quality
16 May 2026 · 4 min read
A 45 MB PDF bouncing back in email is a familiar frustration — the file is too large to attach, too large to send over WhatsApp, and you have no obvious way to make it smaller without losing something. This guide explains what is actually inside a large PDF, how compression works, and how to pick the right quality setting for what you need to do with the file.
Why PDFs get large
Most oversized PDFs are large for one of three reasons, and often a combination of all three:
- Embedded images at full resolution. When you scan a document or export from a design application, images are typically saved at 300 DPI or higher — the resolution needed for high-quality print. Screen display requires far less. A single full-page scan at 300 DPI can exceed 5 MB on its own.
- Embedded font files. PDF stores the complete font data needed to render text correctly on any device. Professional typefaces can be several hundred kilobytes each, and a document using four or five fonts accumulates this overhead even if it uses only a fraction of each font's character set.
- Accumulated revision layers. Documents edited repeatedly in desktop applications often carry ghost data from previous versions — deleted objects, undo history, interim states. Each round of edits without a clean save can add invisible bulk.
What compression actually does
PDF compression is not a single operation — it is several processes applied in combination. Image downsampling reduces the pixel density of embedded images: a 300 DPI photograph is resampled to 150 DPI or 96 DPI, which is imperceptible on a screen but significantly smaller in file size. Images are then re-encoded at a chosen JPEG quality level, trading some detail for much smaller data.
Font subsetting removes unused characters from embedded font files — if your document uses a font that contains 2,400 glyphs but your text uses only 180 of them, the other 2,220 are stripped out. Object deduplication identifies repeated resources (a logo appearing on every page, a repeated background element) and stores them once rather than once per page.
Choosing the right quality setting
Most compression tools offer three or four presets. Here is what they actually mean:
- Maximum compression (screen quality). Images downsampled to 72–96 DPI, JPEG quality around 60%. The result looks perfectly acceptable on a phone or laptop screen. Appropriate for sending by email or sharing a link. Not suitable for printing.
- Medium compression (digital sharing). Images at approximately 150 DPI, JPEG quality around 75–80%. A good balance: the file is substantially smaller, and on most displays you will not notice any difference from the original. This is the setting to default to for most sharing scenarios.
- Minimal compression (near-lossless). Very light reduction, primarily through font subsetting and object cleanup rather than image resampling. Appropriate when the document will be professionally printed, or when you need to retain maximum fidelity.
The practical rule: for anything being read on a screen, 150 DPI is visually indistinguishable from 300 DPI at normal viewing distances. The doubling of DPI quadruples file size with no visible benefit.
When not to compress
There are three situations where compression is the wrong choice. If a document is destined for professional printing — a print shop, a magazine, a product label — always submit the original. If you are compressing a file that has already been heavily compressed (a PDF that was itself exported from a compressed scan), re-compression stacks artefacts and can make the result look noticeably worse than either version alone. And never overwrite an archival original: compress to a copy, keep the master file intact.
What results to expect
Scanned documents — which are essentially photographs of pages — typically achieve 50–70% size reduction at medium quality, because the image resampling is doing most of the work. Text-heavy PDFs with vector graphics tend to see 20–40% reduction, since the text content itself is already stored efficiently and the main gains come from font subsetting and cleanup.
The tool on this site processes everything in your browser. The file is never uploaded — it leaves your device only if you choose to share the result.