How to Compress a PDF to Under 300 KB Online

A 300 KB cap shows up constantly - job application portals, government forms, university admissions systems, and some email attachment filters all impose it. It sounds tiny, and for a PDF full of scanned pages or high-resolution images, it can feel impossible to hit. The good news is that most PDFs can get there with the right approach, and you rarely need to install anything.

Why 300 KB is such a common limit

Many older intake systems and government portals were built around conservative storage budgets, and the limit has just stuck around since. It's usually meant for text-based documents like CVs, cover letters, or forms - not scanned multi-page contracts. That mismatch is exactly why compression is often necessary: a one-page CV with a headshot photo can easily be 2-3 MB straight out of Word or a phone scanning app.

Step 1: Check what's actually making the file large

Before compressing, it helps to know where the size is coming from:

• Embedded images - photos, logos, or scanned pages are almost always the biggest contributor.
• Scanned documents - if the PDF was created by photographing or scanning paper, every page is essentially a large image, which compresses far less efficiently than text.
• Embedded fonts - less common as a major factor, but custom fonts can add tens or hundreds of kilobytes.
• Unused metadata or layers - exported PDFs sometimes carry hidden data from the original design software.

If your file is a text-heavy Word export, compression will likely get you well under 300 KB. If it's a stack of scanned pages, you may need to lower resolution more aggressively, and there's a realistic limit to how small it can go while staying legible.

Step 2: Use an online compressor

For a one-off task, an online PDF compressor is usually faster than digging through print settings in Acrobat. The general workflow is the same across most tools, including the compressor at Konomic:

1. Upload the PDF.
2. Choose a compression level - usually labelled something like "low," "recommended," and "extreme" or "maximum."
3. Run the compression and download the result.
4. Check the file size shown in your file explorer or Finder.

If the first pass doesn't get under 300 KB, re-run it with a stronger setting, or compress the output file again (double-pass compression on scanned image-heavy PDFs can shave off a further 10-20% in some cases, though it doesn't help much on already-optimised files).

Konomic runs this on EU-based servers in Germany, deletes uploaded files automatically within an hour, and doesn't require an account for the compression tool - relevant if the document is a CV with your address and phone number, or a form with personal data you'd rather not have sitting on a server indefinitely. iLovePDF and Smallpdf offer similar compression quality and are worth trying too if you want to compare results, though both push signup prompts more insistently and their processing servers are based outside the EU, which matters if you're handling anything covered by GDPR. Sejda is a solid EU-friendly alternative as well, though its free tier caps you at a lower daily task limit.

Step 3: If you're still over 300 KB

When a strong compression pass isn't enough, try these before giving up:

• Reduce image resolution manually. Most compressors let you pick a target DPI. For on-screen or web viewing, 150 DPI is usually fine; for scanned text you need to read, don't go below 120 DPI or it becomes blurry.
• Convert colour scans to greyscale if colour isn't needed - this alone can cut scanned-page size by 40-60%.
• Split the document if the portal accepts multiple files, and compress each part separately. Sometimes a 10-page PDF stays stubbornly large because one page has a huge embedded photo dragging up the average.
• Re-scan at a lower setting if you have the original paper document and control over the scanner - starting with a smaller file beats compressing a bloated one after the fact.
• Remove unnecessary pages - blank cover sheets, duplicate signature pages, or terms-and-conditions inserts that aren't required.

Step 4: Verify the file still works

After compression, actually open the output file and check:

• Text is still legible, especially small print like dates, reference numbers, or signatures.
• Images haven't become so pixelated that a photo ID or diagram is unreadable.
• The page count and page order haven't changed.
• Any form fields (if it's a fillable PDF) still work - compression tools occasionally flatten interactive fields, which is a problem if the recipient needs to fill something in.

If quality has dropped too far, dial back to a lighter compression setting and accept a slightly larger file, or address the root cause (lower the original scan resolution instead of over-compressing a high-res scan).

A realistic expectation

Text-only documents - CVs, cover letters, short contracts without images - will almost always compress to well under 300 KB, often into the 50-150 KB range. Documents with photos or scanned pages are more variable: a single scanned page at reasonable readability might sit around 80-200 KB per page after compression, so a 5-page scanned form may need image-quality trade-offs to fit under the limit as one file. In that case, splitting the upload or requesting an alternative format (or a higher size allowance) from whoever set the limit is sometimes more practical than squeezing quality out of every page.

A quick checklist

• Identify whether the bulk of the size is images, scans, or fonts.
• Try standard compression first, then a stronger setting if needed.
• Convert to greyscale and lower DPI for scanned pages.
• Re-check legibility before submitting.
• Delete the uploaded copy from whichever tool you used once you've confirmed the result, particularly for documents containing personal data.