You attach a PDF and the email bounces, or the upload form says the file is too large. Before you reach for a tool, it helps to know why the file is big, because that tells you the cheapest way to make it smaller.
Why PDFs get big
A PDF made from a word processor with mostly text is small, often tens of kilobytes. The size comes from pictures. A scan or a phone photo of a page is a full-page image, and a ten-page scan is ten large images. Photos pasted into a document, high-resolution logos and screenshots add up the same way. Fonts embedded in the file add some weight too, but rarely as much as pictures.
That is why two PDFs of the same length can differ by a hundred times in size. Look at yours: if you can select the text with your cursor, it is mostly text; if you cannot, it is mostly pictures, and pictures are what compression can shrink.
Know your limit first
Limits vary. Email providers commonly allow attachments of a few tens of megabytes at most, and the recipient’s server may be stricter than yours. Upload forms often set much smaller limits, such as 100 KB, 200 KB or 1 MB. Work out the number before you start, then work backwards. If the form says “1 MB”, aim a little below, because systems differ on whether that means 1,000,000 or 1,048,576 bytes.
Cheap fixes before compressing
- Send only the pages needed. Split out the pages the form asks for. Removing a page saves more than any compression.
- Delete blank pages. Scanners often add blank backs. Remove blank pages finds them.
- Go grayscale if colour is not needed. Grayscale can make a scan smaller with no loss of information for black-and-white text.
- Rescan with better settings. A scan of text at moderate resolution is far smaller than a high-resolution colour photo of the same page.
Compress with DocPro
- Open Compress PDF and choose your file.
- Pick a quality level, High, Balanced, Small or Smallest, or tick “Aim for a target size” and type the number of KB you need.
- Run it and check the Before and After sizes shown on the result.
- Open the compressed file and read a page at normal zoom before you send it.
The tool re-draws each page as a JPEG picture and saves them as a new PDF. With a target size it lowers quality first, then lowers resolution, until the file fits or it runs out of room to try. If the result is not smaller than your original, it keeps the original and says so. Your file is processed in your browser and not uploaded. Compress PDF is a Pro tool on the web: you can set it up for free, and the final run asks you to sign in to DocPro Pro.
What it costs you
Because pages become pictures, selectable text and links are lost, and the result cannot be searched. Small print can blur at low settings. Always keep your original. Do the compression last: sign, annotate and fill in the form first, because it is hard to edit a compressed copy.
When a target is not reachable
Divide your target by the page count to see the budget for each page. A 100 KB limit across ten pages is about 10 KB a page, which means very soft pages. In that case compression alone will not do it. Options are to split the document, to send it in two files, to put the large attachment in a shared link instead, or to ask whether a larger limit exists. The tool says what size it reached, so you know how close you are.
There are exact-size pages for the most common limits: 100 KB, 200 KB and 1 MB. They open the same tool with the number filled in.
Keep the original. Compression is a one-way trade of detail for size.
Small, targeted changes beat brute force: send fewer pages, drop blanks, avoid colour you do not need, and compress once, at the end.