Choose the compression goal first
PDF compression is not one operation. A document may contain searchable text, vector drawings, forms, links and large photographs. Structure-preserving optimization keeps those capabilities and reorganizes the PDF object streams, while strong compression renders every page and rebuilds it from JPEG images.
Use structure-preserving mode when the PDF remains a working document. Use strong page compression when the priority is a smaller visual copy for email, archiving or screen review.
- Keep the original PDF.
- Try structure-preserving compression first.
- If the result is not smaller, switch to strong compression.
- Inspect text, graphics and every critical page before sharing.
How DPI and quality change PDF size
In strong mode, DPI controls the pixel dimensions of each rendered page. A 120 DPI page contains far fewer pixels than a 200 DPI page and usually produces a smaller PDF. JPEG quality controls compression artifacts inside those pixels. The balanced preset at 120 DPI is a practical starting point for screen documents, not a universal printing standard.
Grayscale can reduce photographic color data further. It should not be used when charts, annotations or brand colors carry meaning.
Privacy and honest limitations
The local PDF compressor reads the selected file with browser APIs and produces a Blob for download. The file is not sent to a server or third-party conversion API. Processing a large PDF still requires enough device memory, and closing other tabs can help.
Strong compression removes searchable text, links, forms, layers and accessibility structure because each page becomes an image. Structure-preserving mode does not deliberately lower image resolution, so an already optimized PDF may stay the same size or become slightly larger.