How to Reduce a PDF's File Size for Online Submission

First, find out why it is large

If the pages are mostly text, the file should be small. If it is large, images are almost always the reason.

• Photos and scans are the most common cause. A single high-resolution page image can take several megabytes.
• Embedded fonts and many separate objects add size, but usually much less than images.
• Very long documents are large simply because they have many pages.

Option 1: export again from the original document

If you still have the Word or Google Docs file, exporting again is usually the most effective fix. In Microsoft Word, the Save As PDF dialog has an option to optimize for minimum size instead of standard quality, which lowers image resolution. Compressing images inside the document before exporting also helps. Check the result on screen to make sure figures remain readable.

Option 2: rescan at a lower resolution

For scanned documents, scanning at a lower resolution, around 150 to 200 dots per inch, is often enough for readable text pages, and grayscale or black-and-white scans are much smaller than colour. If you need text recognition (OCR) later, 300 dots per inch is often recommended, and fine detail such as small diagrams may need more than 200. Check your institution's accessibility or archiving rules first.

Option 3: remove or split pages

If you only need part of a long PDF, extract those pages instead of sending everything. A page range such as 1-3, 8 keeps just the chosen pages. If the system allows several files, splitting a document into parts can also get around a size limit.

What a lossless optimizer can do

A lossless PDF optimizer rewrites how the file is organized internally without changing how any page looks. It can shave off some overhead, but it cannot shrink images, so a scan-heavy PDF may not get smaller at all. A good tool shows the real size before and after, and tells you when nothing was saved. If you need much smaller files, one of the options above, which lower image quality, is usually required.

Know your limit

Upload limits differ widely. Some portals cap each file, others cap the total of everything you attach, and email providers set their own limits on attachments. Read the exact limit on the submission page before you start shrinking, and aim to finish comfortably under it rather than a few kilobytes below. If you have several attachments, add up their sizes.

Check the result before you submit

1. Open the smaller file and look at every page, especially figures, equations and small print.
2. Confirm that text can still be selected if the original allowed it, because some methods turn pages into pictures.
3. Compare the file size with the limit, leaving some margin.
4. Keep the original as your master copy.