You filled one field. The signature stopped counting.
We filled a single field in a signed contract and saved it in Preview on a Mac. The file was rewritten from scratch and the signature no longer matched its bytes. Nothing on screen said so.
Keepsign PDF · for iPhone, iPad and Mac
Fill and sign PDFs without breaking them.
Keepsign checks every save. If a change would invalidate a signature or drop something from your file, it tells you before it saves, and gives you a receipt after.
01 The problem
A PDF can look fine and still be broken.
Most PDF apps rewrite the whole file when you save. On screen nothing changes. Inside, the signature may no longer match, and pieces of the document can be gone.
The text survived. The rest didn’t.
In the same test, saving dropped the file’s attachment, its layer and its page labels. Another popular app removed the signature field altogether, after only saying it would save a copy.
It came back signed. And different.
A contract returns with a signature that looks fine. Somewhere on page 3 a number moved. Unless you reread every line, you won’t notice.
Payment within 30 14 days
Our test, November 4, 2026, macOS 26.5: one signed PDF with a form field, a sticky note, an attachment, a layer and page labels, saved in Preview, PDFgear, PDF Expert and UPDF. Method and results on the comparison page.
02 The promise
Every change, checked. If we can’t keep your document intact, we don’t save it.
ADDED, NOT REWRITTEN
Your original stays byte for byte
Keepsign writes your changes at the end of the file, the way the PDF standard intends for signed documents. What the signer signed is left alone.
CHECKED AFTER EVERY SAVE
It reopens what it just wrote
Then compares it with the file you opened: signatures, fields, pages, notes, attachments, layers. Counted, not assumed.
ASKED BEFORE, NOT AFTER
You decide, with the facts
If a change would make a signature invalid, Keepsign stops and tells you whose signature and why. Nothing gets lost quietly.
03 The receipt
Proof you can keep, and send.
After each save you get a short receipt: what Keepsign checked and what it found. It’s free, on every device, and you can export it with the document.
Keepsign · Save receipt No. A2C4-E826-ECD5
Your signature stays valid 1
Saved and checked at 11:43
Signatures 2
Signature “Ana Ruiz”: validBefore: valid → After: valid, with permitted later changes
What Keepsign checked 3
Still there: JavaScript · attachments 1/1 · layers 1/1 · outline · tagging · XMP
Pages2
Form fields5
Written asAdded at the end
PDF version1.7
KSPDF<<OK<<20261105<<P2<<S1<<A2C4E826ECD5<<< 4
- 1
The verdict, in plain words
“Your signature stays valid.” Or, if something did change, exactly what and on which page.
- 2
Every signature, before and after
Each one is checked against the bytes the signer signed. If the issuer isn’t one your device trusts, the receipt says that too, instead of hiding it.
- 3
What survived the save
Attachments, layers, scripts, bookmarks, accessibility tags and metadata, counted one by one against the file you opened.
- 4
A fingerprint you can check later
A receipt number and the SHA-256 of every version. Export it as a PDF or JSON file and attach it when you send the document.
04 Hard to find elsewhere
Six things the big PDF apps don’t do.
We looked at the App Store pages, websites and help of the PDF apps people use most. Each claim below says what we checked and when.
01
A receipt for every save
What was kept, what changed, and whether each signature still holds. Free, every time.
How the receipt worksTested Nov 4, 2026 in Preview, PDFgear, PDF Expert and UPDF: none reported what it kept.02
A warning before a signature breaks
Keepsign tells you whose signature a change would invalidate before it writes anything.
Signing without breakingSame test: none of the four warned before saving.03
“What changed?” for PDFs you receive
Every save in the file’s history, changes after a signature word by word (“30” → “14”), and text hidden or drawn on top.
Spot an edited PDFApp Store search for “pdf tamper”, “detect edited pdf” and “pdf forensic”, Nov 2026: no consumer app does this.04
AI that stays on your device
Ask a contract a question and get an answer with the page and the sentence. Keepsign checks each quote is really there.
Private AIPDFgear’s and PDF Editor’s AI work over the internet, by their own pages; PDF Expert’s privacy notice lists cloud AI providers.05
Digital ID signatures on iPhone and iPad
Sign with your certificate (.p12 or .pfx) on every device, free, in the PAdES format.
Certificate signaturesAcrobat and PDFgear do it on Mac only; PDF Expert doesn’t offer it (their help pages, Nov 2026).06
Shortcuts and Spotlight that know your documents
19 Shortcuts actions, and Spotlight finds a PDF by what’s inside it, its type, and the next date that matters.
All featuresNone of the five top-grossing PDF apps mentions Shortcuts on its App Store page or recent notes (Nov 4, 2026).05 Everything else
All the tools you expect from a PDF app.
Reading, filling, signing and saving are free and stay free. Pro adds the power tools, once.
Sign SIGN
- Draw, type or use a photo of your signatureFree
- Initials, dates, initials on every pageFree
- Digital ID (certificate) signaturesFree
- Verify signatures, with the chain and timestampFree
- As many saved signatures as you need, each with its namePro
Fill FORMS
- Fill any form, also XFA and flat onesFree
- My Info autofill, calculations, flattenFree
- Turn a flat PDF into a fillable formPro
- Import and export form data, templatesPro
Annotate MARKUP
- Highlight, notes, shapes, text boxes, imagesFree
- Pen, marker, lasso and Apple PencilFree
- Redact by hand, for realFree
- Measure distances and areas with a scalePro
Edit EDIT
- Edit text like in a word processorPro
- Find and replace, edit imagesPro
- Page numbers, headers, watermark, BatesPro
- Organize, rotate, insert, extract, merge pagesFree
Convert EXPORT
- PDF to Word, Excel and PowerPointPro
- Tables from scans to a spreadsheetPro
- PDF/A for archivingPro
- Images, documents and web pages to PDFFree
- Export pages as images or textFree
Scan SCAN
- Scan paper with searchable textFree
- Make an existing PDF searchablePro
- Erase pen marks, stains and holesPro
- Fix scans, both sides of an ID cardPro
Send SHARE
- Review before sendingFree
- Remove personal info, passwordFree
- Ready to send: under 10 MB or 2 MBPro
- Find and redact sensitive dataPro
Review CHECK
- What changed? and compare versionsPro
- Ask, summarize, dates and deadlinesPro
- Accessibility check with fixesPro
- Versions, and recovery after a crashFree
Read READ
- Read aloud, also with the screen lockedFree
- Translate, reflow, presentFree
- Search, outline, sepia and night modesFree
06 One app
iPhone, iPad and Mac. One purchase.
The same Keepsign on all three, built for each: Apple Pencil on iPad, windows and tabs on Mac, the share sheet on iPhone. Pick up where you left off with Handoff, keep your PDFs in the Keepsign folder in iCloud Drive.
Works the way Apple devices work
- Share sheet: sign or check a PDF from Mail or Files
- Finder and Quick Look show the seal on signed files
- Widgets, Control Center and the Action button
- 19 Shortcuts actions and Siri
- Spotlight finds PDFs by what’s inside
- Read aloud keeps going with the screen locked
iOS 17, iPadOS 17 or macOS 14 or later. The AI tools need a device with Apple Intelligence.
07 Price
Free to fill and sign. Pay once for the rest.
Keepsign
$0
Everything you need to read, fill, sign and send safely.
- View, search, read aloud, translate
- Fill forms and annotate
- Sign, also with a Digital ID
- Save without breaking, with the receipt
- Password, versions, recovery
- 1 saved signature and 1 initials
Keepsign Pro
US$29.99once
The power tools, for good. Try any 3 Pro jobs free first.
- Edit text, convert to Word, Excel, PowerPoint
- Compress to a size, OCR, erase marks
- What changed?, compare, on-device AI
- Batch jobs, Bates, PDF/A, measure
- iPhone, iPad and Mac, with Family Sharing
- Every future version included
For Teams
US$49.99per licence
For companies and schools that deploy with Apple Business or School Manager and an MDM.
- Everything in Pro, no in-app purchase
- Settings locked by your MDM
- Save-error reports to your MDM, no content
- 50% off for schools buying 20+
Price in US dollars. The App Store shows the price for your country. Keepsign PDF for Teams is coming after the main app.
08 The numbers
What paper, fakes and subscriptions cost.
Every figure has its source and date in the article behind it.
28dayslost per employee each year to printing, signing and scanningAdobe survey, 1,500 UK workers, 2022
1 in 16documents checked by lenders in 2025 flagged as fraudulent; AI fakes up nearly fivefoldInscribe, 2026 Document Fraud Report
$519a year for a $9.99-a-week PDF plan left runningApp Store prices, Nov 4, 2026
2 hyour file stays on a popular free PDF site’s servers, by its own policyiLovePDF security page; FBI warning, March 2025
09 Guides
Signed PDFs, explained.
Free answers to the questions that bring most people to a PDF signature.
SignaturesSign without printingThe steps on iPhone, Mac, Windows and Android, whether it counts, and when a drawn signature isn’t enough.SignaturesVerify a PDF signatureSigned or just signed-looking, how to verify it for free, and what to look at besides “valid”.SignaturesWhy a signature shows invalidThe real meaning of valid, invalid and unknown, and the fix for each cause.SignaturesSign without invalidatingWhich changes a signed PDF allows, why most apps break it anyway, and how to add yours safely.
10 Questions
Questions people ask first.
Is Keepsign free?
Yes. Reading, filling forms, annotating, signing (also with a Digital ID), saving without losing anything, the save receipt and passwords are free, with no watermark and no time limit. Keepsign Pro is a single purchase of US$29.99 for the power tools, and you can try any three Pro jobs before you decide.
Does it really keep signatures valid?
When the change is one a signature allows, such as filling a field or adding a note, Keepsign adds it at the end of the file and the signature keeps covering what was signed. Some changes can’t be made without invalidating a signature, for example rewriting text on a signed page. In that case Keepsign tells you before saving, and you choose.
Is a signature made with Keepsign legally binding?
That depends on your country, the kind of document and who receives it, so we can’t promise it. What Keepsign does is make sure the signature you add, and the ones already there, aren’t damaged by saving, and it shows you how each one checks out.
Do my documents leave my device?
No. Keepsign has no account and no server. Converting, OCR, compression and the AI all run on your iPhone, iPad or Mac. Your files only go where you send them, or to your own iCloud if you keep them there. The privacy page lists every exception, such as the optional online certificate check.
Which devices does it run on?
iPhone and iPad with iOS or iPadOS 17 or later, and Macs with macOS 14 or later. One purchase covers all of them. The on-device AI needs a device that supports Apple Intelligence; everything else works without it.
Is there a subscription?
No. Pro is a one-time purchase, shared with up to five family members through Family Sharing, and future versions are included.
Can I use it for my company or school?
Yes. The free app works for anyone. For managed devices there is Keepsign PDF for Teams, with Pro included and settings your MDM can lock.
Get one email when Keepsign is out
One message on launch day, then we delete your address. No newsletter. How we handle it.