ZenConverter

1. What is ZenConverter?

ZenConverter is a free Android app that converts files right on your phone, without uploading them to any website. You pick a file, choose the format you want, and the app processes it on the device and saves the result. According to the documentation there are no ads, no accounts and no payments, and the conversion itself sends nothing over the network. The app is written in Kotlin and licensed AGPL-3.0.

What it can do (from the official support matrix; "Stable" routes were verified on a real device):

• PDF: merge several PDFs into one, compress a PDF (three levels: high quality, balanced, small file), set or remove a PDF password (removal only works if you know the password), extract text to TXT/MD, and turn each page into an image.
• Images: convert between JPG, PNG, WEBP and ICO; turn images into PDF (several images into one PDF); upscale images (including an AI mode that downloads a model when needed); view and strip hidden data (EXIF, GPS location) from JPG photos.
• Video and audio: convert MP4/MKV/MOV/WEBM, compress video, merge several videos, trim clips, make an animated GIF from a video, extract the audio track to MP3/M4A/WAV/FLAC/OPUS, and convert between audio formats.
• More: convert subtitles (SRT, VTT, LRC, ASS), convert fonts (TTF, OTF, WOFF, WOFF2) and turn Word/PowerPoint/Excel files into PDF (a "Beta" feature).

A good fit if:

• You often need to merge, compress or convert PDFs, photos or videos on your phone and do not want to hand private files to online converters.
• You want an app with no ads and no sign-up.

Not a good fit if:

• You use an iPhone. This is an Android app only.
• You need text recognition (OCR) for scanned pages. The documentation says there is no OCR; a scanned PDF with no text layer fails when you convert it to TXT.
• You need Word/PowerPoint/Excel converted to PDF with exactly Microsoft Office's layout. That feature is Beta; the documentation warns that complex files can come out with shifted text or shapes, and source files are capped at 64 MiB.
• You want a Vietnamese interface. Available languages are English, Simplified and Traditional Chinese, and French. There is no Vietnamese yet.
• You want to convert very large videos on a weak phone. The documentation warns that large videos need enough free storage, memory and battery, and that you should keep the device free while a long conversion runs.

2. What you need

• An Android phone or tablet running Android 8.0 or newer (the source sets the minimum at Android API 26, which is Android 8.0).
• A 64-bit ARM chip (arm64-v8a). The APK ships only this build. Most current Android phones use it. Devices with other chips (some old tablets or emulators) may not be able to install it.
• Storage: the APK is about 38 MB (measured 12 Oct 2026, version 0.2.4). You also need free space for the output files, especially video. The AI upscaler downloads a model when you turn it on (for example about 4.65 MB for the compact one and 63.9 MB for the high-quality one, per the support matrix).
• Internet: only to download the app, check for updates manually, and download AI models or fonts when you ask for them. Converting files does not use the network.
• No account, no API key, no cost.

3. Step-by-step install

There are two official routes. Route 1 is easiest for newcomers.

Route 1: Install from Google Play (recommended)

Step 1: Open the app page

On your phone, open https://play.google.com/store/apps/details?id=org.zenconverter.app (the Google Play link that the project's GitHub page points to), or open Google Play and search for ZenConverter. Check the developer and the exact app name, because Google Play has many look-alike converter apps.

Step 2: Install

Tap Install, wait for the download, then tap Open. You know it worked when you see the app's main screen for adding files.

Note: The Google Play version number may differ from the newest GitHub release. The documentation does not say the two are always in sync.

Route 2: Install the APK from GitHub

Use this if your phone has no Google Play or you want the newest build.

Step 1: Download the APK

On your phone, open https://github.com/Jasonzhu1207/ZenConverter/releases/latest and download the file ending in .apk under Assets, named like ZenConverter-v0.2.4-arm64-v8a.apk (the version may be newer). Download only from this page.

Step 2: Allow installs from your browser

When you open the APK, Android usually asks for permission to "install unknown apps". Tap Settings in the prompt and allow it for the app you used to download the file (for example Chrome or Files). Menu names vary by phone brand.

Step 3: Install and open

Open the APK again, tap Install, then Open. If Google Play Protect shows a warning, read it carefully and continue only if the file came from the GitHub page above. After installing, turn the "install unknown apps" permission off again for that browser.

The release description lists the APK's SHA-256 checksum if you want to compare it.

4. First use

Example: merge two PDFs into one.

1. Open ZenConverter and add files with the add-file button. The app receives files through Android's file picker, or you can open or share a file from another app into ZenConverter. You can pick several files at once, including from the photo gallery or a whole folder.
2. Select the two PDF files. For each file or for the group, the app lets you choose what to do (merge, compress, convert to images, set a password...) and its options.
3. Start the job. Progress shows per task in the queue and you can cancel midway. Longer jobs run in a background service, so keep the phone free and do not close the app until it finishes.
4. When it is done, the result appears in the list; from there you can share the file or try to open the file or its folder.

You did it right when the result opens in your PDF reader app and has all the pages of both files.

A few tips from the documentation: PDF compression has three levels (High Quality, Balanced, Small File) and keeps text selectable; a separate privacy tool shows hidden data in JPG photos (such as GPS location) and can remove it without re-encoding the image, and can restore it for that same image.

5. Common problems and fixes

Symptom	Cause	Fix
"App not installed" or the APK will not install	The phone is not arm64, runs Android below 8.0, or already has a build signed with a different key (for example the Google Play version)	Check the requirements in section 2. If the Google Play version is installed, uninstall it before installing the APK, or the other way round (reinstalling loses the app's data)
The APK cannot be installed because it is blocked	Installing from unknown sources is not allowed yet	Allow installs for the browser or Files app that opened the file, as in step 2 above
A video conversion fails or stops halfway	Not enough storage or memory, or the phone killed the background app to save battery	Free up space, plug in the charger, keep the screen on and turn off battery saving for ZenConverter. Try a short clip first or lower the resolution in the options
PDF to TXT fails	The PDF is a scan with no text layer	The app has no OCR. Use a separate OCR tool, then convert
A HEIC/HEIF file will not convert	This depends on your phone's image decoder (a Beta route)	Try another phone or shoot in JPG
AI image upscaling errors out or is very slow	The model must download on first use and runs on the GPU, and results vary by chip	Connect to the internet to download the model, try the compact model first, or use the normal 2x, 3x or 4x upscaling
Word/PowerPoint to PDF has a shifted layout	It is a Beta route and does not promise Microsoft Office fidelity	Check the result; for important documents export the PDF from the Office app itself

6. Uninstall and update

• Uninstall: go to Settings → Apps, choose ZenConverter and tap Uninstall; or long-press the app icon and choose uninstall. Result files you saved are not deleted with it.
• Update (Google Play): open the app page on Google Play and tap Update (or turn on auto-update).
• Update (APK): download the newer APK from the releases page and install it over the old one. The documentation also says the app has a manual update check.

7. FAQ

Does it cost anything? No. According to the documentation there are no ads, accounts or payments.

Are my files sent anywhere? According to the project, conversion runs on the phone and sends no data over the network. The INTERNET permission is used only for manual update checks and for downloading models or fonts when you ask. That is the project's own statement; the source code is public so it can be checked.

Does it need the internet? Only to download the app, to download AI models or fonts, and to check for updates.

Does it work on an iPhone or a computer? No, it is an Android app. For PDFs on a computer, see PdfCraft on githot.

Will it run on a weak phone? Converting photos and PDFs is usually light. Large videos, AI upscaling and frame interpolation need a stronger phone; the documentation says results depend on the chip, memory and free storage.