PDF & Documents
Why your PDF is huge - and how to shrink it
A three-page contract should not weigh 15 MB. Almost every oversized PDF has one of four causes, and once you know which one you have, getting under a portal's 1 or 2 MB limit is straightforward.
Key takeaways
- Scanned pages stored as high-resolution images are the number one cause of bloated PDFs.
- Text-based PDFs exported from Word are usually small already - if yours is not, embedded photos or fonts are the culprit.
- Reducing image resolution inside a PDF to 150 DPI keeps documents perfectly readable on screen.
- Digitally signed PDFs must not be restructured - compress before signing, not after.
The four reasons PDFs get big
- Scans stored as images: a page scanned at 300-600 DPI in color is a 2-8 MB image. Ten pages, 40 MB. This is by far the most common cause.
- Embedded photos: a report with a few smartphone pictures inherits their full 3-5 MB each unless the export resizes them.
- Embedded fonts: each fully-embedded font family can add hundreds of kilobytes - noticeable in small documents.
- Duplicated or unused objects: editors that merge, stamp or re-save PDFs often leave dead weight (old page versions, unused images, form leftovers) inside the file.
What actually helps, in order
The FileSizeFix PDF compressor does the safe parts of this automatically and locally in your browser: it analyzes the page images, recompresses them toward your KB target and cleans redundant structure - without sending the document anywhere.
- Recompress page images. Downsampling scans to 150 DPI and re-encoding them as JPEG typically cuts scanned PDFs by 60-90% with no visible loss on screen.
- Resize embedded photos before export when you control the source document - a picture displayed at 8 cm width never needs 4000 pixels.
- Remove dead weight: a clean re-save drops unused objects, old page versions and redundant metadata.
- If the PDF is born from images anyway (photos of documents), build it directly to a KB target instead of shrinking afterwards.
What compression cannot do
Honesty matters here: a PDF that is already text-only with efficient fonts barely shrinks - there is nothing left to compress. And a scan that was already aggressively compressed may only lose a few percent more before artifacts appear.
Digitally signed PDFs are a special case. Any structural change invalidates the signature - which is correct behavior, not a bug. Compress first, sign second. The same applies to PDFs with fillable forms you still need: flatten or compress carefully, and always check the result before submitting.
Hitting exact portal limits
Application portals love round numbers: 500 KB, 1 MB, 2 MB. Two tricks help. First, check before you upload - a size checker tells you instantly whether the file passes a given limit. Second, compress toward a target slightly below the limit (for example 950 KB for a 1 MB portal), because some portals measure size in ways that add a little overhead.
Realistic targets by document type
If your file sits far above its row, compression will close the gap. If it is already inside the range, further squeezing mostly buys artifacts - consider splitting the document or asking whether the limit can take a second file instead.
| Document | Pages | Realistic compressed size |
|---|---|---|
| Text-only contract (born digital) | 1-10 | 50-300 KB - often already there |
| CV with one photo | 1-2 | 150-500 KB |
| Scanned certificate, grayscale | 1-2 | 200-600 KB |
| Scanned contract, color | 5-15 | 1-3 MB |
| Image-heavy brochure | 10-30 | 3-10 MB |
Frequently asked questions
How do I get a PDF under 1 MB?
Use a compressor that recompresses the page images, which is where the weight lives. Scanned documents usually reach 1 MB easily at 150 DPI; born-digital text PDFs are typically under 1 MB already.
Does compressing a PDF reduce its quality?
Screen readability survives 150 DPI recompression easily. Fine print in large-format plans or documents meant for high-quality printing deserve a gentler target - or no recompression at all.
Why did my signed PDF stop validating after compression?
Compression rewrites the file structure, which breaks the cryptographic signature by design. Always compress before signing.
Is it safe to compress confidential PDFs online?
With classic upload-based services you are trusting a third-party server. The FileSizeFix compressor processes the PDF locally in your browser instead - the file never leaves your device.