Compressed PDF blurry? Why it happens, and how to get it sharp

The short answer: four things to try, in this order

A PDF gets smaller by storing its pictures with fewer dots. That is fine for a photo seen on a phone, and it shows on a page of small print. If your compressed copy looks soft, try these, starting with the first:

1. Start again from your original, not from a copy that was already compressed. Detail lost once is lost for good.
2. Pick a higher level on the PDF compressor: Recommended (150 ppi) instead of Smallest (100 ppi), or Best quality (220 ppi) for printing.
3. Send fewer pages, if you're squeezing a long scan under a size limit. Fewer pages means more room for each.
4. Check the smallest print that matters (a roll number, a date, a seal) on the saved file, before you send it.

Your original is never changed, so you can try each level and keep the copy you like best. Everything runs in your browser, and nothing is uploaded. The rest of this post explains why blur happens and what each fix does.

If your trouble is a file that is too big rather than too soft, How to reduce PDF file size without losing quality goes through the ways to make it smaller.

First, find out whether yours is typed or scanned

The compressor never turns text into pictures. Text, fonts, lines and vector drawings are left alone, so they stay as crisp as in the original, and you can still search and copy the text. Only pictures are resized: photos, scans, and pictures like a logo or a scanned signature.

So the question is whether your pages are text or pictures:

• Typed PDFs, such as a bank statement, a certificate downloaded from a portal or a letter saved from Word, are mostly text. They can't turn blurry from compression. If a typed page looks soft, the cause is somewhere else, such as a small screen or a zoomed page.
• Scanned PDFs are a picture of each page. These are the ones that can get softer.

To tell, open the file in the PDF viewer and try to select a line of text, or search for a word. If you can't select anything, or search says "No text", the page is a picture. A page that looks slightly tilted, grey or speckled is also usually a scan.

If you see blur on a typed PDF after compressing, check one more thing: a page can mix both, such as a typed form with a scanned signature or a photo pasted into it. Only the picture will be softer.

What each level keeps

The levels decide how sharp the pictures stay. ppi means pixels per inch: how many picture dots fill one inch of the page. More dots mean a sharper picture and a bigger file. Pictures sharper than your level are scaled down to it, and saved again as JPEG at a matching quality.

Pictures that are already below the level are not changed. A colour A4 page scanned at 300 dpi is about 8.7 million pixels, and each scanned page took 1 to 2.5 MB in our test files. A quarter of those pixels, 150 per inch, already looks sharp on a screen or an office printer. So if your copy came out blurry at Smallest, try Recommended first. Best quality is for printing photos, and the file stays bigger.

Charts, logos and screenshots with few colours are kept sharp with lossless compression, so they don't blur at any level.

What a number of ppi really looks like

Numbers are hard to picture. These are measured on scans of A4 pages made at 300 dpi, which we put under a size limit with our exact-size pages and then opened at normal screen zoom:

The scale those pages use: Sharp is 150 ppi or more, Good is 100 or more, Readable is 45 or more, and Rough is anything below. "Readable" is a wide band. Near the top, a page looks almost untouched. Near the bottom, ordinary print is fine but small print struggles. This is also why Smallest (100 ppi) is a sensible choice for reading on a phone but a poor one for a page you plan to zoom into.

Read more in What a page looks like under 200 KB. The pages in those tests were scans. Typed text is not affected by any of this.

The more pages, the less room for each

If you're squeezing a long scan under a size limit, the limit is shared by all the pages. A 200 KB limit gave this in our tests:

What decides how a page looks is the room each page gets. So the quickest way to a sharper copy is to take out pages the form doesn't need: blank backs, cover pages, instructions printed on the reverse. Use Split PDF to pick the pages you need. If the form lets you, send the long file in parts, so each part gets its own limit. See How many pages stay clear in 200 KB for the full table.

If the limit is exact, Resize PDF keeps trying until the file is within 15% under your limit, which gives the sharpest version that fits.

Don't compress a compressed copy

Every round of compression loses a little picture detail. That's the most common reason a file looks worse than expected: it was squeezed for one form, then squeezed again for another. The second round starts from a file that has already lost detail.

• Keep your first scan or your first PDF in a safe folder, and never overwrite it.
• Start from it every time. If one place wants 100 KB and another wants 2 MB, make each from the original, not from each other.
• Check the name before you start. A file called final-compressed-small.pdf is probably not your best copy.

And in the other direction: the compressor reads the new PDF back to check every page is still there, and if the new file would not be smaller, you keep your original. So trying it costs nothing.

Signatures, stamps and colours

Thin lines and light colours are the first things to fade when a page gets less room. Stamps and seals are made of the same thin lines and light colours, so expect a faint stamp to fade before a strong, dark one. In our tests, a blue signature stayed blue and clean on one page and on four pages, and turned grey on fourteen.

A few habits help before you scan:

• Sign with a dark blue or black pen, not a light ballpoint.
• Make sure the stamp is clear on the paper. A smudged stamp only gets worse.
• Scan at 200 to 300 dpi. A higher setting makes a huge original without making text easier to read.
• Scan in colour if the form doesn't say. We compared a grayscale copy of a four-page colour contract with the colour one under 200 KB. The colour scan came out at 99 ppi and the grayscale at 102 ppi, a gain of less than 3%, but the blue signature turned grey. Grayscale helps little and costs the colour.

Check the saved file before you send it

This takes a minute and avoids a rejected form:

1. Open the compressed file in the PDF viewer or your usual reader. Don't judge from the small preview in a file list.
2. Pick Fit width for reading, or 100%, where a page shows at about the size it would be on paper.
3. Find the smallest text that matters: a roll number, a date of birth, an amount, a seal.
4. If you can't read it comfortably at 100%, go back to the original and try a higher level, or fewer pages.
5. Look at the first and last pages too, since a long scan can vary.

If the receiver only has to read the file on screen, Recommended is almost always enough. If they will print it, or look at fine detail, use Best quality for that copy.

If you still can't get it sharp enough

• Is the file too big to send at all? For email, Gmail takes attachments up to 25 MB and sends anything bigger as a Google Drive link, so you may not need to shrink it much. The post Compress PDF for email goes through the limits.
• A form with a tight limit? Upload the clearest pages, and look at the form's notice. The form's own rules always win.
• The scan itself is soft? Compression can't add detail that isn't there. Scan again, closer and in better light, then compress.
• Why is it so big to begin with? Why is my PDF so large? lists eight causes and how to fix each.

Try each level without sending anything

The compressor has no upload step, so trying three levels costs no waiting and shares nothing. Your file is read, compressed and saved on your own device. The page contacts only this site and Google's ad service, which shows the ads that keep the tools free, and our code never gives your files to the ad code. The privacy policy has the details.