How to sign and lock a PDF without uploading it.

Open the PDF; if your iPhone asks, open it in the Files app and tap Save. Tap the Add button, then Add Signature, sign with your finger, tap Done and drag the signature into place. Your iPhone keeps it for next time. In Notes and Photos, Add Signature is in the Markup toolbar.

To lock it on iOS 26 and later, open it in Preview, tap the Actions Menu button next to the filename, then Lock, and type the password twice; on iOS 26, turn on Require Password too. Tap Done. To keep an unlocked copy, tap Duplicate in that menu first. Apple says a lock keeps others “from editing or deleting your work.”

For a paper form, see how to scan documents to a PDF; to join files first, see how to merge PDFs on an iPhone.

Open the PDF in Preview, show the Markup toolbar, and click Sign. Make a signature on the trackpad, by holding it up to the camera on white paper, or on a nearby iPhone or iPad, then drag it into place. With iCloud Drive, it appears on your other Macs.

For a password, choose Export from the File menu and click Permissions. Select Require Password To Open Document and type it twice, then set an owner password, which controls printing and changes. Click Apply, then Save.

Microsoft Edge has a PDF reader built in. Microsoft says its inking “comes in handy to take quick notes for easy reference, sign, or fill out PDF forms,” and the PDF toolbar saves a copy with your markings. Edge can check a certificate-based signature, but Microsoft doesn’t describe making one.

Microsoft’s pages on Edge don’t describe adding a password. Word on Windows can encrypt a document as it saves it as a PDF: under Options, choose Encrypt the document with a password.

• Adobe Acrobat Reader, a free app, signs with a drawn, typed or pictured signature. A password needs a paid plan: Acrobat Standard is $14.99 a month on a yearly plan.
• Adobe Acrobat online signs and adds a password for free. The file goes to Adobe’s servers and is deleted unless you sign in to save it, and its signing steps say you must be signed in to complete the form.
• Smallpdf signs with no account and locks with AES 128-bit encryption. It deletes files after one hour, and its free plan has a daily download limit.
• iLovePDF’s free plan signs 3 files and locks 2 a task, and its FAQ says it keeps files “for a maximum of 2 hours.” A certified Digital Signature needs Premium, $5 a month billed yearly.

Adobe calls an electronic signature “any electronic mark that indicates a person’s intent to sign a document,” typed, drawn or pictured. A digital signature “uses a certificate-based digital ID to verify the signer’s identity and detect any changes made to the document after signing.”

Everything here makes the first kind, PDF Kit included. Adobe says that’s legally sufficient for most business contracts, leases and HR documents under US law, and Docusign says some businesses, regions and uses may require digital signatures. If you’re sent a signing link, use it: Docusign says signing with it is always free.

PDF Kit is ours. Sign takes a signature drawn with a finger, a pen or a mouse, or your typed name, and puts it where you tap, with today’s date if you like; a drawn one is kept on your device for next time. Add a password uses AES-256 and lets you allow or block printing and copying text, which most PDF apps respect. Files are opened in your browser, never uploaded, and it works offline once opened.

It isn’t free: Sign and Add a password come with implements, $4.99 a month or $49.99 a year for every tool. Only merging up to 3 PDFs and splitting one are free. On a Mac, or an iPhone with iOS 26, Preview signs and locks for free; PDF Kit helps most on Windows, where Microsoft’s guides give Edge no password option.