How Browser PDF Compression Works

A transparent look at how FileForge shrinks PDFs in your browser via page rasterization — what it preserves, what it trades away, and when to use it.

Runs entirely in your browser — no uploads

The question everyone asks

"Why did my compressed PDF lose selectable text?" It's a fair question, and it deserves a straight answer about how browser-based compression actually works — including what FileForge does, why, and when you should use something else.

Two fundamentally different approaches

Server-side recompression. Full PDF engines can parse a document's internals, re-encode embedded JPEGs at lower quality, subset fonts and discard redundant objects — keeping text as live, selectable text. This requires a heavyweight engine, which is why services that do it typically run it on servers (and charge for it).

Browser-side rasterization. FileForge's Compress PDF takes a different route: it renders each page to an image at a resolution you choose, then rebuilds a fresh PDF from those optimized images. Pages look essentially identical, but the payload is now efficient imagery instead of sprawling document structures.

Why we chose rasterization anyway

  • It runs entirely in your browser, consistent with the site's core promise: your file never uploads. A full fidelity-preserving recompression engine would mean shipping tens of megabytes of code to every visitor.
  • It's predictable. Image-based output renders the same everywhere — useful for scans, presentations and image-heavy decks, which are exactly the files people most want to shrink.
  • It offers honest control. You choose High/Medium/Low quality and see the before/after sizes before downloading.

The trade-off, stated plainly

Rasterized pages are pictures of pages. Text in them can't be selected, searched or copied, and zooming past the rendered resolution won't reveal more sharpness. For a scan you're emailing, that's irrelevant. For a 300-page reference manual you intend to search forever, it's the wrong tool.

A decision guide

Your fileGood fit?
Scanned document, already imagesExcellent — nothing textual is lost
Slide deck or brochure, image-heavyVery good with Medium/High quality
Text report you need to search laterPoor — use High quality only, or seek a desktop recompressor
Form you still need to fill digitallyWrong tool — rasterizing kills form fields

Tips for best results

  1. Always compare the reported before/after size — a file that barely shrinks wasn't the compression type's target anyway.
  2. Use High when the PDF will be printed or archived; Low suits quick previews.
  3. Need to reclaim pages afterwards? Split PDF and PDF Page Organizer both work happily on compressed output.

The bigger point

Every tool has limits; trustworthy tools disclose theirs. We'd rather tell you exactly what Compress PDF does to your file than quietly upload it somewhere for "better" results you can't audit. That's the deal local-first makes: capability trade-offs in exchange for control.