How to Reduce PDF Size to 100, 200 or 500 KB

Why the PDF is so big

Almost all the weight in a big PDF comes from pictures. A scanner app or a phone camera saves every page as a large photo, so ten scanned pages can easily be several MB. A PDF made from Word or a website is usually small, but it can still grow because of the fonts stored inside it. Hidden extras add a little more: page thumbnails, metadata and leftovers from earlier edits.

How to compress a PDF for an online form

1. Check the limit the form gives, then open the matching tool: Compress PDF to 100KB, 200KB or 500KB.
2. Press Select PDF, or drag the file onto the box. You see its size straight away, and whether it is already under the limit.
3. Press Compress to under 200 KB (or 100 or 500). A progress bar shows each step. Big scans can take a minute, so keep the tab open.
4. Read the result: the size before, after, and how much was saved, in KB and in exact bytes.
5. Press Download PDF. The new file is named like yourfile_under_200kb.pdf. Your original is not changed.
6. Open the new file and zoom in on the smallest print before you upload it.

The PDF is read and compressed inside your browser. It is not uploaded, which matters for mark sheets, ID cards and bank papers.

Is 200 KB 200,000 or 204,800 bytes?

Websites do not agree on this, so the tool plays safe. It counts 1 KB as 1000 bytes and stays one byte below the limit, which passes on any site. The size it shows uses 1024 bytes to a KB, the way most upload forms show it, so it reads a little lower than the limit.

What the compressor actually changes

It works in steps and stops at the first one that gets the file under the limit. If the PDF is already small enough and nothing can be gained, you get the original back untouched.

1. Clean-up without any loss: hidden metadata, page thumbnails and leftovers of earlier edits are removed, and parts that were stored uncompressed are packed. Nothing you can see changes.
2. Smaller pictures: photos and scanned pages inside the PDF are made smaller in pixels and saved as JPG at a lower quality. There are 13 settings, from a longest side of 2400 pixels at high quality down to 440 pixels at low quality. The tool tries the strongest one first to see whether the limit can be reached at all, then searches for the mildest one that still fits. So the file keeps as much detail as the limit allows. Text that is real text is not touched.
3. Pages as pictures: only when shrinking the pictures is not enough, for example a text PDF with heavy fonts, every page is saved as one compact picture. Pages with photos become a JPG, from 150 DPI downwards. Pages with only text and lines become a sharp black-and-white picture, which keeps letters crisp at a tiny size. Page order, size and orientation stay the same.

After step 3, the text in the PDF can no longer be selected, searched or copied, because each page is now a picture. Most forms only need the page to be readable, so this is usually fine. Every result is measured, and it is only called done when it really is under the byte limit.

What usually fits

A rough guide only. The real result depends on how the PDF was made, how much colour it has and how busy the pages are.

When it cannot get small enough

Sometimes even the strongest setting is too big. The tool then says it could not get the PDF under the limit and offers the smallest version it made, so you can see how close it came. A very long file can also fit, but at such a low resolution per page that small print becomes hard to read. In both cases, try these, in this order:

• Remove pages the form does not need, such as blank backs, instructions or a cover. Fewer pages leave more room for each one.
• Split the PDF and upload the parts separately, if the form has more than one upload box.
• Use the next size up if the form allows it. 200 KB looks much better than 100 KB for a multi-page scan.
• Scan again with a closer crop. Borders, the desk and shadows all cost space. Dark ink on plain white paper compresses best.
• Start from the original scan, not from a copy that was already compressed somewhere else.

Limits worth knowing

• One PDF at a time, up to 100 MB and 500 pages.
• Password-protected PDFs cannot be opened. Open the file with its password and save or print it as a new PDF first.
• Black-and-white fax-style scans are left as they are, because they are already small. Images in CMYK or special colour spaces are also left unchanged.
• The search for the best setting stops after about 3 minutes and keeps the best file so far.
• If the tab closes or freezes, the file was too big for your device's memory. Close other tabs, use a computer, or split the PDF first.

If a portal still refuses a file that is under its stated limit, its real limit may be lower than it says. Compress again with the next size down, or remove one page.