Frequently Asked Questions


Q: What is

A: We are the owner of - a popular online converter website. When we were developing, we noticed some disadvantages of online converter and started to develop an offline converter. Thanks to new technologies such as ES Modules, WebAssembly, Shared Array Buffer, and Site Isolation, it's possible to convert files offline in web browsers now. This website was created many years ago, but it's delayed to be published until most web browsers on the market start to support the new technologies.

Q: Why files can be converted offline in web browser?

A: Files can be converted by Javascript or WebAssembly in web browser. WebAssembly is a type of code that can be run in modern web browsers - it is a low-level assembly-like language with a compact binary format that runs with near-native performance and provides languages such as C/C++, C#, and Rust with a compilation target so that they can run on the web. It is also designed to run alongside JavaScript, allowing both to work together.

Q: Is secure?

A: Yes, is secure to use. Offline converter is the opposite of online converter, it's for maximum protection of your privacy because all files are converted locally instead of on cloud servers. You don't need to worry about the leak of your files. The WebAssembly we use is a safe technology. WebAssembly describes a memory-safe, sandboxed execution environment that may even be implemented inside existing JavaScript virtual machines. When embedded in the web, WebAssembly will enforce the same-origin and permissions security policies of the browser.

Q: How to convert files on

A: Converting files on is as simple as 1-2-3.

  • 1. Click the "Choose Files" button to choose local files on your local device.
  • 2. Choose a target format and set conversion options if needed.
  • 3. Click the "CONVERT OFFLINE" button and wait for the conversion to complete. The output files will be listed on the same webpage.
Q: What file formats does support?

A: You can check supported file formats at Please note this is just a small list of file formats supported by, many unpopular file formats supported are not listed. For example, supports about 80 image formats while only the top popular image formats are listed. You can directly convert these unpopular formats on without any problems.

Q: Why can't I convert Word, Excel, or PowerPoint to PDF offline on

A: requires the converter software used in the web browser to be open-source, small in size, and compatible with compilation into WebAssembly/Javascript. We use Microsoft Office to convert Word, Excel, and PowerPoint files online on, Microsoft Office is property software, big in size, and cannot be compiled into WebAssembly/Javascript.

Q: What platforms and web browsers does support?

A: You can use on any operating system (such as Windows, Linux, Mac OS, Android, or iOS) that has a modern web browser. The web browser can be Chrome 57+, Edge 16+, Firefox 52+, Safari 11+ or Opera 44+. However, Internet Explorer is not supported.

Q: What are the conversion limitations?

A: You can choose an unlimited number of files each time, each file size can be up to 2 GB.

Q: Why is the first file conversion slow?

A: It needs to load javascript before the first file conversion. For video and audio conversions, the javascript can be up to 32mb. It may take a while to download the javascript from the server if the internet connection is slow.

Q: Why is the conversion slower compared to desktop software?

A: As of now, WebAssembly/Javascript is still a lot slower than native, it is possible to further speed up using WebAssembly intrinsic, which is basically writing assembly code. It is something we are investigating and hope to introduce in the future. Another reason that causes conversion slow is that uses a single thread by default. Using multithread may consume a lot more memory or CPU, and it requires additional security measures such as Shared Array Buffer and Site Isolation.

Q: Why did my conversion fail?

A: Most conversion failures are caused by incompatible web browser or OS. We recommend upgrading your OS and web browser to the latest version. There are also many other reasons that may cause conversion failure, for example: the source file is not supported, corrupted, encrypted with password, or Digital Rights Management (DRM). Try online converter instead if this offline converter doesn't work in your web browser.

Q: How can I save all output files in one ZIP file?

A: To save all output files in one ZIP file, simply click the "Compress files" button in the "OUTPUT FILES" section.

Q: How can I delete all output files?

A: To delete all output files, simply close the webpage in your web browser. All output files will be cleared immediately and can't be recovered.

Q: Which one should I choose, offline converter or online converter?

A: is an offline converter, so we recommend offline converter:) You can check the comparison of offline converter and online converter at the index page and choose a suitable converter for yourself.

Q: I have more questions, who should I write to?

A: Please send your additional questions to and will usually get a response in one business day if it's question about file conversion, other questions may be ignored.

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