Why does my signature look blurry on a PDF signed on iPhone?

You signed the PDF on your phone, sent it off, and either you or the person who received it opened it and saw a signature that looks like a photocopy of a photocopy: soft edges, grey fuzz around the strokes, maybe a faint rectangle of off-white paper behind it. The rest of the document is perfectly crisp. Just your name is a smudge.

This almost never means your phone did anything wrong. It means the signature was an image, and somewhere between drawing it and viewing it, that image got stretched or squashed. There are four common ways that happens, and they have different fixes. Work down the list in order; the first one costs nothing and solves it for a lot of people.

First: are you looking at the file, or a preview of it?

Before you redo anything, check where the blur is. Mail, Messages, WhatsApp and most web browsers show you a quick preview of an attachment, not the PDF itself, and previews are rendered small and compressed. A signature that looks fuzzy in the Mail preview can be perfectly sharp in the actual file.

On your iPhone, save the PDF to Files and open it there, or open it in Books. Pinch to zoom in on the signature. If it sharpens as you zoom, the file is fine.
Better still, open it on a computer at 100% zoom. That is how most recipients will see it.
If the recipient says it’s blurry on their end, ask them to download the attachment rather than preview it in the email window.

If the signature is sharp in the real file, there’s nothing to fix, and sending a new copy would produce exactly the same result. Only carry on if the blur survives this test.

Cause 1: the signature started life as a small photo

This is the big one. If you photographed a signature on paper, or screenshotted one, or used a signature image someone sent you, the result is a bitmap with a fixed number of pixels. A cropped signature from a phone photo might only be a few hundred pixels wide. Scale that up to fill a signature line on a letter-size page and every pixel gets stretched; the strokes go soft and the edges of the ink turn into grey staircases.

Compression makes it worse. A signature saved as a JPEG, or sent through a chat app that recompresses images, picks up blocky artefacts around the strokes that look like dirt once it’s enlarged.

How to tell: zoom into the signature in the finished PDF. If the strokes have visibly square or blocky edges, or there’s a faint greyish box around the ink, you’re looking at an upscaled or compressed image.

The fix: go back to the source and capture it bigger and cleaner. Sign large on plain white paper with a dark pen, in good light, and photograph it close so the signature fills the frame. The full routine is in how to turn a signature on paper into a digital signature with your iPhone. Then remove the paper background and save as a PNG, not a JPEG, so you don’t get a white box or compression noise: how to make a transparent signature PNG covers that step. A signature image that’s a couple of thousand pixels wide can be placed on any normal signature line without softening.

Cause 2: it was drawn small and dragged big

If you drew the signature with your finger, the tool you used decides whether it can be resized without blur.

A signature drawn directly in iOS Markup is stored as strokes, so you can drag its handles to any size and it stays sharp. If you drew it in Markup and it still looks blurry, the blur is coming from somewhere else on this list.

A signature drawn in an app that saves it as a picture, though, has a fixed resolution the moment you save it. Draw a one-centimetre scribble, save it, then stretch it across a line four times as wide, and you’ve done the same thing as Cause 1 by hand. Apps vary a lot here: some save the drawing at screen resolution, some at a multiple of it, and the difference shows the moment you enlarge it.

How to tell: the signature looked fine while you were drawing it and only went soft after you placed and enlarged it.

The fix: draw it at roughly the size it will sit on the page, or bigger, rather than tiny. If the app lets you, draw with the canvas zoomed in, so a comfortable finger-drawn signature ends up with plenty of pixels behind it. Then size it down, never up. Sizing a signature down is always safe; sizing it up is where blur comes from. How to resize a signature on a PDF on iPhone covers the handles and what size actually looks right on a line.

Cause 3: the whole PDF was sent as a picture

Sometimes the signature is blurry because the entire page is. If you signed the PDF and then shared a screenshot of it, or printed it and photographed the print, or ran it through a scanner app and sent the scan, the recipient didn’t get your PDF at all. They got a photo of it, and photos of documents are always softer than the document, with the thinnest lines (which is to say, your signature) suffering first.

How to tell: the printed text on the page is slightly soft too, not just the signature, and the file arrived as a JPEG or as a PDF that won’t let you select text.

The fix: share the PDF file itself. Every signing route on iPhone, Markup included, hands you back a real PDF; use the share sheet to send that, and never a screenshot of it. If someone sent you a scan to sign, that page was already soft before you touched it, and the best you can do is keep your signature sharp on top of it. How to sign a scanned document on iPhone is about exactly that case.

Cause 4: the signature has been through too many hops

A signature you made in 2019, emailed to yourself, screenshotted off a laptop, cropped in Photos and have been pasting ever since has been resampled half a dozen times. Each hop loses a little. This is the same as Cause 1, just slower, and the fix is the same: make one clean, large, transparent PNG of your signature, store it somewhere you can find it, and never derive a new copy from a derived copy. The free signature generator exports a transparent PNG directly if you’d rather draw a fresh one than scan paper.

What about Signed?

Signed is a PDF signing app for iPhone, and here’s exactly what it does about blur, including where its limits are.

When you draw a signature in Signed, the app saves it as a PNG at three times screen resolution, cropped tightly to the ink. That is enough pixels for a signature-line-sized placement to come out crisp on screen and in print, and because the image is trimmed to the strokes with no paper behind it, there’s no off-white box around the ink. It is still a raster image, though, not a vector. If you stretch it across a whole page width you will eventually see it soften, so the honest advice is the same as above: size it to the line, not larger.

When you scan or import a signature, Signed keeps whatever resolution the source photo had. The on-device cleanup straightens the paper, lifts the ink onto a transparent background and crops in tight, which removes the grey box and the paper tint, but it cannot invent detail the camera never captured. A sharp capture in, a sharp signature out; a blurry phone photo in, a cleaner but still soft signature out.

On export, Signed draws your signature into the page at the size you placed it and produces a flattened PDF, the file itself, which you share from the share sheet. That closes off Cause 3. Everything happens on the phone; the document never leaves your iPhone.

The thing that makes the most difference, in Signed or anywhere else, is that you create the signature once and well, then reuse it. Blur is a symptom of remaking or re-copying your signature every time you need it.

The two-minute check before you send

Open the finished PDF in Files or Books, not a mail preview.
Zoom in on the signature. Crisp strokes, no grey box, no blocky edges.
If it fails, don’t resize the blurry one. Replace it with a sharper source using the cause above that matches, and sign the original unsigned PDF again.

Signed is a signing tool, not legal advice. A blurry signature is a cosmetic problem, not a validity problem, but if a document matters, a recipient who can’t read your name may ask you to redo it, so it’s worth the two minutes.