How to compress a PDF without choosing the wrong trade-off
First decide what must survive: searchable text, a fillable form, crisp diagrams or only a readable scan. Compress PDF offers image compression and a separate Preserve text and vectors mode. These operations have different consequences.
Choose a mode from the source
- Photographic scan: try Balanced image compression on a working copy. Inspect the smallest text and faint stamps.
- Selectable report text: start with Preserve text and vectors. It attempts a structural rewrite; an already compact file may not shrink.
- Interactive or digitally signed document: keep the original and check the recipient's rules before rewriting it. Image mode loses selectable text, interactive forms, links and signature validity.
Run a controlled comparison
- Record the original byte size and page count. Pick a small representative PDF, within 50 MB. Image rendering supports up to 150 pages.
- Process a copy with the chosen mode. Change one setting at a time so you know what affected the result.
- Compare the displayed input and output sizes. If compression did not help, the tool can offer the original; a successful run is not proof of a reduction.
- Check every output page, zoom into small print and try selecting a sentence when selectable text is required.
A useful small-file experiment
Try the two-page practice PDF in Preserve text and vectors mode. It is a small synthetic report, not a compression benchmark. A tiny input may already be efficient. The important check is whether the downloaded result remains readable and whether its actual size is better, not whether an arbitrary percentage was reached.
What custom image settings mean
Enable Use custom image settings before adjusting resolution and quality. Lower settings can reduce detail; higher settings use more memory and do not recreate missing information. Grayscale may remove meaningful colour distinctions. Compare a test copy before processing a long scan.
When a portal still rejects the result
There is no guarantee of 500 KB or another target. If the destination allows multiple attachments, split into measured parts. If it accepts only one file, obtain a more efficient source scan or use an appropriate document application. Splitting into several files does not satisfy a one-file requirement.
Updated October 29, 2026 · PDF Tools Club. Examples use synthetic documents; keep your own originals.