In Bitrix24, you can choose how documents are viewed. To do this, open the module settings and select an option in View documents using.

Each option works differently:

• Bitrix24.Docs
  Work with files in the cloud. You can create, view, and edit files in these formats: .pdf, .docx, .doc, .rtf, .xls, .xlsx, .xlt, .ppt, .pptx, .pptm, .xodt.
  Other file types open in the Bitrix24 viewer.
  This option requires an active license, Disk module version 21.800.0 or later, and additional setup. The number of documents you can edit at the same time is limited.
• Bitrix24
  Use the built-in viewer. It supports local viewing for files such as .pdf, .mp3, .txt, .php, .css, .html, some .mov and .mp4 videos, and all image formats.
  Other file types are converted using the Bitrix24 cloud service. Files are not stored in the cloud—they are only processed for viewing. No user data or file source information is saved.
• Google Docs
  View files through Google Drive. Sign in to your Google account and set up Google Drive. Files are temporarily uploaded to your Google Drive and opened in Google Docs.
• Office 365
  View files using Microsoft services. This option works similarly to Google Docs.
• Google Viewer
  Generate a public link to view the file. The link is deleted automatically after use. Performance depends on Google.

Important:
All of these options send data to external services. If you don’t want this, turn off Enable document editing using external services (Google Docs, MS Office Online, etc.).

To prevent files from being sent to external servers when using the Bitrix24 viewer, remove the Transformer module. This disables file conversion.

If you use a self-hosted Bitrix24 Enterprise edition, you can set up a local document conversion server in a Bitrix Virtual Appliance.