What happens when you upload a PDF to sign it
With a typical web-based signer, your browser sends the PDF to the service's servers. The server renders it, adds your signature, and sends back a finished file. Some tools do more of the work inside your browser, but you can't tell which kind you're using just by looking at the page.
After you upload a file, what happens next depends on the company. It decides how long to keep it, who can access it, whether to back it up, and whether to use it for anything else. A good service explains all of this plainly. Others leave it vague.
What on-device means
An on-device app opens, signs, and saves the PDF using your phone's own processor. The file doesn't need to travel anywhere, and it only leaves when you choose to share it. eSign PDF works this way. There's no account, and signing and flattening work in airplane mode.
"Native app" doesn't automatically mean private, though. An app can still upload files or collect data. Check its App Store listing, where the App Privacy section lists the data the developer says it collects. Then try the airplane-mode test below.
What to look for in a privacy policy
You don't need to read every word. Search the policy for these points.
- ✓Retention. Is there a specific time limit for deleting uploaded files, or just "as long as necessary"?
- ✓Use of your documents. Are files used only to deliver the service, or also to improve products or train models?
- ✓Sharing. Which third parties or subprocessors can access files, and for what?
- ✓Location. Where the company stores and processes the files.
- ✓Account and deletion. Whether you need an account, and how to delete your files and data.
- ✓Specific claims. "Processed locally in your browser" is a clear statement. "We take your privacy seriously" isn't.
Browser tool vs on-device app vs Apple Markup
| Feature | Typical web signer | eSign PDF (on-device) | Apple Markup |
|---|---|---|---|
| Where the file is processed | Often on the service's servers | On your iPhone | On your iPhone |
| Account | Often required or pushed | None | None |
| Works offline | No | Yes | Yes |
| Flattened export | Varies | Yes | No, signature is an annotation |
| Dates, checkboxes, initials | Varies | Yes | Text boxes only |
| Price | Varies, often free with limits | $59.99 once | Free |
Two quick tests you can run yourself
- 1Airplane-mode test (apps). Turn on airplane mode, open a PDF in the app, sign it, and export it. If it all works, the signing is happening on the phone.
- 2Network test (websites, on a computer). Open your browser's developer tools, go to the Network tab, then load and sign a test PDF. Large outgoing requests while the file loads usually mean the site is uploading it. Use a dummy file for this, not your real lease.
When a browser tool is fine, and when it isn't
For a sign-up sheet, a flyer, or anything you'd happily email to a stranger, a reputable web tool is fine. Use whatever is easiest. Many web services handle files carefully, delete them quickly, and say so clearly. Uploading isn't wrong in itself. The point is to know what you're agreeing to.
The stakes change with what's on the page. A leaked restaurant order form costs you nothing. A leaked W-9 or bank form can mean someone opening accounts in your name. You also can't take a file back once it's on someone else's server.
Keep the file on your phone when the PDF contains your Social Security number or EIN (W-9, W-4) or bank or income details. The same goes for a lease with your application data, medical or school records, or a client's confidential terms under an NDA. See signing tax forms on your phone, and for the basic workflow, how to sign a PDF on iPhone. Apple's free Markup is also on-device. Its limits are flattening and form fields, covered in Markup vs a signing app.
Free websites vs a paid app
eSign PDF: $59.99 one-time (US), no account, works offline. Apple Markup: free, also on-device. The App Store shows other plans and local prices.
FAQ
Do online PDF signers upload my document?+
Many do. They send the file to their servers to process it. Some work mainly in the browser. The privacy policy, or a network test with a dummy file, will tell you which.
Is it safe to sign a W-9 on a website?+
It can be, if the service is reputable and clear about retention and deletion. Because a W-9 carries your SSN, many people prefer an on-device tool.
How can I tell if an iPhone app works on-device?+
Turn on airplane mode and try signing and exporting a PDF. Also check the App Privacy section on the app's App Store listing.
Does eSign PDF upload my files?+
No. Signing, filling, and flattening happen on your iPhone. There's no account. Files leave only when you share them.
Is Apple Markup private?+
Yes, Markup runs on your device. Its limits are different: signatures are annotations that some non-Apple viewers don't show, and it has no real date or checkbox fields.