Why is my PDF so large (and how to fix it)

Cause 1–2: scans and photos (90% of cases)

A page scanned at 300–600 DPI in color is a huge image — a few pages easily reach tens of megabytes. Likewise, a Word document with phone photos dropped in produces a PDF carrying each photo at full camera resolution, even if it is displayed at thumbnail size.

Fix: compression with image downsampling. At reading size, re-encoding those images to screen resolution is visually indistinguishable and routinely cuts 50–90% of the size.

Cause 3–4: embedded fonts and duplicated resources

Full CJK font files embedded in a document can add several megabytes each. Merging PDFs from mixed sources can also duplicate the same image or font across sections. These matter less often than images, but they explain the mystery of a text-only PDF that is still 8MB.

Cause 5: hidden data

Deleted-but-retained objects, embedded thumbnails, metadata and editing history all linger inside the file. Rebuilding the document during compression drops unreferenced objects; a metadata cleaner also removes XMP metadata if privacy is the concern.

Not sure which cause applies? Just run the compressor: its pre-run estimate (computed locally, no quota) immediately shows how much is recoverable — a big estimated saving means images, a tiny one means the file is already tight.

Step by step

1. 1

   Run the compressor for a diagnosis

   Drop the PDF (processed locally, never uploaded). The pre-run estimate shows how much can be saved.

2. 2

   Big saving available? Compress

   Images were the cause. Standard level keeps reading-size quality; target-size mode hits a hard limit.

3. 3

   Barely shrinks? The file is already tight

   The tool tells you honestly when compression would not help — and consumes no quota.

4. 4

   Privacy concern? Clean metadata too

   Use the PDF metadata editor to view and clear document metadata including XMP.

FAQ