Why PDF files get so large
PDFs grow large primarily because of embedded images. A scanned document, for example, is essentially a series of high-resolution photos wrapped in a PDF container. Each page can be several megabytes. Other contributors include embedded fonts, vector graphics, and metadata.
How to compress a PDF for free
- Go to signvert.com/tools/resize-file.
- Select "PDF" as the file type and drop your PDF onto the page.
- Choose a compression preset: High Quality (minimal compression), Balanced (recommended), or Small File (maximum compression).
- Click "Compress" and download the result.
The tool re-renders each PDF page as a compressed image and reassembles them into a new PDF. This works best on scanned or image-heavy PDFs.
How much can you compress a PDF?
Results vary significantly depending on the content:
- Scanned documents: 60–80% size reduction is common.
- Image-heavy PDFs: 40–70% reduction.
- Text-only PDFs: Minimal reduction (5–15%), because text is already very compact.
Compressing images (JPG, PNG)
The same tool handles image compression. Upload a JPG or PNG, set the quality slider (80% is a good starting point — usually invisible to the eye), and optionally set a maximum dimension. A 4 MB phone photo can typically be reduced to under 500 KB at 80% quality.
When compression isn't enough
If a PDF is large because it contains many pages, consider splitting it first using our Split PDF tool and only sending the relevant pages. For scanned PDFs, running OCR (via our PDF to Word tool) and saving as a text-based PDF produces much smaller files than image-based scans.