How MendPDF handles your files
MendPDF is built on a local-first architecture. This page explains exactly what happens to your files when you use each tool, in plain language, with no marketing ambiguity.
Core principle: local-first processing
The majority of MendPDF tools process your documents entirely inside your web browser using WebAssembly (WASM) technology. Your file is loaded into browser memory, processed locally, and the result is generated on your device. No document data is sent to any server for these tools.
Tools that process locally
These tools run entirely in your browser. Your file never leaves your device. When you close the browser tab, the file is discarded from memory.
What happens technically
Inside your browser's memory, using a compiled WebAssembly (WASM) engine based on PDFium. The engine runs locally. No server communication occurs during processing.
No. The file is read directly from your device into the browser. It is never transmitted over the network.
No. The file exists only in browser memory (RAM) during your session. When you close the tab or navigate away, the data is discarded.
No. Since the file never leaves your device, MendPDF has no access to your document content. There are no analytics, logging, or telemetry on document data for local tools.
The PDF editor uses a PDFium-based WASM engine that patches the PDF content stream directly. It supports incremental save, preserving the original document structure. All of this happens inside your browser.
Magic Scan: the exception path
Magic Scan is the one workflow where a temporary server relay is involved. This is because your phone and your desktop browser need to exchange a file across devices. Here is exactly what happens:
What happens technically
Your phone browser and your desktop browser cannot communicate directly. A temporary encrypted relay bridges the gap so the scanned file can move from one device to the other.
Yes. The file is encrypted end-to-end before it leaves your phone. The relay server receives only encrypted data and cannot read the document content.
The encrypted file is automatically deleted from the relay server after 60 seconds, whether or not it has been downloaded.
No. The encryption keys are generated in your browser and never sent to the server. The relay handles only encrypted bytes it cannot decrypt.
Once your desktop browser downloads and decrypts the file, it exists only in browser memory, the same as all other local tools. The relay copy is deleted.
What MendPDF does not do
Browser compatibility
MendPDF requires a modern browser with WebAssembly support. All major browsers have supported this since 2017.
For the best PDF editing experience, we recommend using a desktop browser. Mobile browsers support viewing and basic operations.
Legal documents
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Questions about privacy or security?
We welcome questions about how MendPDF handles files. Privacy and security inquiries are reviewed with appropriate priority.
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