Frequently asked questions

No. Every tool runs inside your browser tab. The PDF engine is compiled to WebAssembly and executes on your own processor, so the file is read from your disk into the tab’s memory and never crosses the network.

Open any tool, wait for it to finish loading, then disconnect from the internet and use it. It keeps working. You can also open your browser’s developer tools, switch to the Network tab, and confirm no request carries your file.

We cannot. Your file is never transmitted to us, so there is nothing to store. When you close or reload the tab, the browser frees that memory and the file is gone.

That is exactly the case the architecture is designed for. Because the document never leaves your device, using ZasPDF does not constitute disclosure to a third party or an international data transfer. You remain responsible for the file on your own machine and for how you share the result afterwards.

Two different things are involved. Your browsing of the website is measured with Google Analytics and monetised with Google AdSense, like on any ad-supported site. The contents of your files are never collected, because they never reach us. Our analytics events record only which tool was used, never a filename or its contents. The privacy policy lists every cookie individually.

No. Every tool works without signing in. An account is optional and only stores your email address, display name and profile photo through Google Firebase Authentication.

WebAssembly is a low-level format that browsers can execute at close to native speed. It is what makes local PDF processing practical: the same Go code that would normally run on a server is compiled to WebAssembly and runs in your tab instead, with no server involved.

Any current version of Chrome, Edge, Firefox, Safari or Opera, on desktop or mobile. WebAssembly has been supported across all of them for years. Very old browsers without WebAssembly support cannot run the tools.

The PDF engine is a single binary that has to download before it can run. It is fetched once and then cached permanently, so every later visit starts instantly. The delay only reappears if we ship a new engine version.

There is no fixed limit, because there is no server to impose one. The practical ceiling is your device’s memory: the whole document has to fit in the tab. We show a warning above 100 MB. On a typical laptop, files in the low hundreds of megabytes work; very large scanned documents can exhaust the tab’s memory.

Almost always the tab ran out of memory. Try closing other tabs, using a desktop rather than a phone, or splitting the document into smaller parts first and processing them separately.

Once a tool page has loaded, yes. The engine is already in the browser cache and needs no network access to do its work.

Yes, the site is designed for mobile browsers. There are also native iOS and Android apps that share the same processing engine. Bear in mind that a phone has far less memory than a laptop, so very large files are more likely to fail there.

The standard mode runs a structural optimisation: it removes duplicated and unused objects, cleans up the cross-reference table and rewrites the file more compactly, without touching the visual content. Your text stays text and stays selectable. The aggressive mode is different — it renders each page to an image and rebuilds the PDF from those images, which shrinks the file much further but turns text into pixels.

Structural optimisation can only remove redundancy that exists. A PDF exported cleanly from modern software often has very little of it, so there is nothing to reclaim. Files that shrink dramatically are usually ones assembled by older tools or repeatedly edited. If the bulk of your file is high-resolution scanned images, the aggressive mode is the one that will make a difference.

No. Unlocking requires you to supply the correct password; the tool then decrypts the document and writes an unprotected copy. It is a convenience for documents you are entitled to open, not a way to break encryption on documents you are not.

Protecting encrypts the file so it cannot be opened or modified without a password. Signing places a visual signature — drawn, typed or uploaded — onto the page. Signing does not encrypt the document, and protecting does not indicate who approved it.

English and Spanish. The tool downloads the language model for whichever you pick. Accuracy depends heavily on the scan: clean, straight pages at 300 DPI or higher read well, while low-resolution, skewed or handwritten pages read poorly.

PDF describes where marks sit on a page; it does not record paragraphs, tables or styles. Any conversion has to infer that structure, so the result is a reconstruction rather than a copy. Text-heavy documents convert well; multi-column layouts, complex tables and heavy graphic design do not.

It produces a visual signature image placed on the page, which is what most everyday agreements and internal approvals call for. It is not a cryptographic digital signature with a certificate from a trusted authority. If your situation demands a qualified electronic signature, use a certified provider.

It is free and the site is funded by advertising, which is its only source of revenue. There is no trial, no per-tool charge and no feature locked behind a paywall.

Neither. There is no cap on how many files you process and nothing is stamped onto your documents. Since the work happens on your own hardware, there is no server cost for us to ration.

Eleven: English, Spanish, Portuguese, French, German, Italian, Japanese, Simplified Chinese, Traditional Chinese, Hindi and Arabic, with right-to-left layout for Arabic.

Through the contact page. This is a small project, so those messages reach the person who builds it directly.