Disclosure first: PicToPDF is our app. That is a reason to be sceptical of the recommendation at the end, not a reason to distrust the table, which describes things you can check yourself in about five minutes.
Start with what is already free
Before installing anything: iOS converts photos to PDF through the print sheet, and through Create PDF in the Files app. Android does it through the Save as PDF virtual printer. Both are free, both work offline, both handle a batch.
What neither gives you is control over page order, page size or output quality. If you do not need those, stop reading and use the built-in route.
The comparison
Prices move, so this table describes the model rather than a number. Check the store listing before you commit to anything.
| Option | Model | Files leave device | Page order control | Best at |
|---|---|---|---|---|
| iOS print trick | Built in, free | No | No | One off conversions |
| Files, Create PDF | Built in, free | No | Folder order only | Images already in Files |
| Android Save as PDF | Built in, free | No | No | One off, with paper size |
| Microsoft Lens | Free, Microsoft account optional | Optional | Yes | Photographing documents and whiteboards |
| Google Drive scan | Free with a Google account | Yes, to Drive | Yes | Scans you want in Drive anyway |
| Adobe Acrobat mobile | Free tier plus subscription | Yes for most features | Yes | Editing PDFs, not making them |
| Web converters | Free tier plus subscription | Yes, uploaded | Usually | Desktop, occasional use |
| PicToPDF | Free to try, in app purchase | No | Yes | Camera roll batches, HEIC, PDF back to images |
The picks
Photographing a document: Microsoft Lens
It is free, it has no account requirement for the basic path, and its edge detection and contrast handling are better than most paid apps. If your job is receipts, forms and whiteboards, this is the answer and it costs nothing.
Occasional conversion of a photo you already have: the built-in route
Do not install anything. The print trick takes five taps and produces a fine PDF.
Regular batches from the camera roll: a dedicated converter
This is the case the built-in tools handle worst, because they give you no control over the order and no way to see the pages before export. It is also the case this site is built around.
Reading the paywall before you hit it
The App Store shows in app purchases on the listing page, under the price. Two things worth checking before you import fifty photos into something.
Is the limit on conversions or on features? An app that gives you three free conversions is a trial. An app that gives you unlimited conversions and charges for OCR is a free tool with an upsell. Both are legitimate, and they feel completely different to use.
Is there a watermark on the free tier? This is the one that ruins an afternoon, because you find out after the export. A watermarked PDF cannot be sent to anyone, which means the free tier is a demo rather than a tool.
Our own answer for the record: the web tool here is capped at one conversion a day on iPhone and five on Android and desktop, with no watermark. The app is free to download and charges for unlimited use.
Apps against websites
The real difference is not features, it is where the file goes.
A traditional web converter uploads your image to a server, converts it there, and hands back a download. That is a reasonable design and it is how most of the well known ones work. It also means a copy of your photo existed on somebody else's disk, however briefly, and their retention policy is a paragraph in a document you did not read.
A browser converter that runs locally, like the one on this site, does the work in your own tab. You can verify it: load the page, turn off your network, convert anyway. It works, because there was never a server involved.
An app is local by default and adds the thing a web page cannot have, which is direct access to the camera roll. That is the whole argument for installing one.