OnlyOffiice

[derei]

I could only find the app on Google Play: https://play.google.com/store/apps/details?id=com.onlyoffice.documents

And this is their website: https://www.onlyoffice.com/download-desktop.aspx#mobile

[DarkCrypt]

It looks like the website only points to the Play Store. The app is available from multiple sources (APKPure, APKMirror, Uptodown, etc.).

GitHub also has releases.
https://github.com/ONLYOFFICE/documents-app-android

Edit:
For apps only found on the Play Store, I highly recommend using Aurora Store.

[DwainZwerg]

My order would rather developer website > Codeberg/Forgejo > GitLab > GitHub > F-Droid Third-Party (if it is from the developer) (> Ascreescent (currently not yet available)) > F-Droid > AuroraStore > F-Droid Third-Party (if it is not from the developer) > IzzyOnDroid (> apkmirror (because it is always track-only, I also use another store)) > APKPure > up-to-down > aptoide. In addition, I normally set all other available AppSources as track-only.