Optimise a PDF for the web — linearise it for fast first-page display

How to use the PDF optimizer

1. Drop a PDF onto the box or press Choose a file.
2. Press Optimise for web. There are no settings.
3. Read the summary, which shows the size before and after, and download the copy. It is named with -web added, so brochure.pdf becomes brochure-web.pdf.
4. Upload the new file to your website in place of the old one.

What it does and when to use it

When a PDF is linked from a web page, a normal file must arrive completely before many viewers can draw anything, because the index of a PDF is stored at the end. A linearised PDF puts the first page’s content and a page index at the start. If the web server supports partial downloads (byte-range requests, which most do), the browser’s viewer can display page 1 within a moment and fetch later pages as you scroll.

This matters most for long, heavy files people open from a link: product catalogues, menus, annual reports, course packs and manuals. For a file you only send by email, linearising gives no benefit, and compressing or extracting the pages you need helps more.

How it works

The tool runs qpdf, a widely used open-source PDF toolkit, compiled to WebAssembly (the @neslinesli93/qpdf-wasm package), inside a background worker in your browser. pdf-lib is also part of the tool. The file is passed to qpdf with three instructions:

• --linearize: write the file in linearised order with hint tables.
• --object-streams=generate: pack small objects together into compressed object streams.
• --compress-streams=y: make sure content streams are compressed.

qpdf then writes a new file that describes exactly the same document. Nothing is re-rendered or re-encoded, so image quality and text are untouched.

Worked examples

A 12-page report. A 5.2 KB test report made by a PDF library gives Linearised for fast web view · 5.2 KB → 5.9 KB. The hint tables cost a little space on a file this small.

A 40-page catalogue for a website. The summary shows the size before and after. Upload the -web copy in place of the old file; a viewer that loads PDFs in parts can now show page 1 before the rest has arrived.

Limits and tips

• The benefit depends on the server and viewer supporting partial downloads. If either does not, the file simply loads as normal.
• Password-protected files must be unlocked first with Unlock PDF.
• Editing a linearised file later (adding pages, filling a form) usually removes the linearisation. Optimise as the last step before you publish.
• To shrink scanned or photo-heavy files to a set size, try compress PDF to 1 MB.