Make a PDF smaller without uploading it

A PDF full of scans or photos can be too big to email or to send through an upload form. PDF Assembler makes it smaller on your own computer, so the file doesn't have to go to a website first.

How to do it

1. Open PDF Assembler and drop the PDF onto the window. One file is enough.
2. Click Next, and Next again, to reach the Save step.
3. Set Quality to Smaller. If the result is still too big, try Smallest instead.
4. Click Save PDF and give the file a new name, so the original stays as it was.

When it's done, the app shows how much smaller the file got. If you're emailing it, you can add a password in the same step: open Advanced options and set Protect to Standard (AES-128) or More secure (AES-256).

What gets smaller

Compression works on the images inside the PDF: scanned pages, photos and screenshots. Text, fonts and drawings are left as they are, so text stays sharp and you can still select and search it. That's why the saving depends so much on the file. A PDF made of photos or colour scans often shrinks by 85 to 95%. A report exported from a word processor is mostly text, is small already, and hardly changes.

A scan that was already compressed hard has little left to give. If compressing wouldn't make a file smaller, the app leaves it as it is.

Smaller or Smallest

Smaller re-encodes the images at a high quality, at up to about 144 dots per inch, and on screen the difference is usually hard to see. Try it first. Smallest squeezes them harder, at about 110, which suits scans and photo-heavy files you only need to read. For a file that will be printed, choose Smaller or keep the original. Open the saved file and zoom in on a scanned page, to check the small print is still easy to read before you send it.

What to keep the original for

The smaller copy keeps every page and its fillable forms, but not extras such as bookmarks or attached files. For a stack of scans that makes no difference. For a long report with bookmarks, or an e-invoice with a file attached, keep the original and send the smaller copy.

Why do it on your own computer

An online compressor needs the file on its servers first. For a payslip, a medical letter or a signed contract, that upload is the part worth avoiding, and there's a longer page on what an upload sends. PDF Assembler reads the file from your disk and saves the result back to it, and it works without a network connection.

About PDF Assembler

PDF Assembler is a small app for macOS and Windows that merges, splits, compresses and password-protects PDFs on your own computer. It makes no network requests at all. It's paid once, with no subscription, and the store links are on the product page.

Other guides: Combine photos into one PDF, Merge PDFs on Windows without Acrobat.