Why PDFs Get Large
The main cause of oversized PDFs is embedded images. When you scan a document or export a presentation, the resulting PDF stores full-resolution image data for every page. A 300 DPI scan of a 10-page document can easily reach 20-40MB. Other factors include embedded fonts, color profiles, bookmarks, and duplicate data objects. Text-only PDFs are usually compact. The size problem almost always involves scans, photos, or graphics-heavy exports.
How PDF Compression Works
PDF compression re-samples and re-encodes images embedded in the document. Lossless compression reorganizes how data is stored without discarding pixels. Lossy compression goes further by reducing image resolution to a level not visible at normal screen or print size. Text and vector graphics are never degraded regardless of compression level. Only raster images are re-sampled. Charts, diagrams, and typed text always look identical before and after.
Choosing the Right Compression Level
Low compression reduces file size by 20-40% with no visible change. Use this for print-ready documents. Medium compression targets 50-70% reduction and is the right choice for most sharing situations. Documents remain crisp on screen and acceptable for standard office printing. High compression maximizes size reduction. For scanned text pages, the difference is rarely visible because original scan resolution far exceeds screen display needs.
Step-by-Step: Compress a PDF Online
Open the ToolMint Compress PDF tool in your browser. Click Upload or drag your PDF into the upload area. Select a compression level. Click Compress and wait a few seconds. Download the compressed PDF and verify the new file size. If the file is still too large, split the document into sections first using the Split PDF tool, compress each part separately, then recombine with Merge PDF.
When You Should Not Compress a PDF
Court-filed legal exhibits with specific DPI requirements must stay at their original resolution. Print-ready artwork destined for a commercial printer should keep its full image data. PDF/A archive files have strict structural requirements. Also avoid compressing a file multiple times. If a file is already under 500KB, there is no practical benefit to compressing it further.