There are a few methods for sharing files in Bitrix24:
Attaching a file to a post in the Activity Stream
To attach a file to a message in the Activity Stream (Image1), enter the recipients (the default is set for everyone) and click the paper clip to open the file upload interface. Upload a file or files by dragging them fr om your file manager onto the upload interface or by clicking on the interface and browsing to the file(s). After the file is uploaded, you will be able to choose wh ere it should be saved (in the message itself, in your personal files, in a group or in Shared Documents).
When the message is sent, each addressee receives notification via Instant Messenger and the post will appear in the Activity Stream only of addressees. Access to the message itself and the attached file will be granted only to users shown in the To: field. After the message is sent, users can view the file and discuss it directly in the Activity Stream. If the file is saved in a document library, discussion can likewise go on in the document’s detail page.
Uploading a file to a document library
A document uploaded to a document library (personal, group, or Shared Documents) will be visible in the Activity Stream for users who have access to the given file.
The item in Activity Stream can be bookmarked, subscribed to, commented upon, or liked (Image2).
Sending a link to a file
If a document is already located in a library and you need to point it out to a colleague, you can either send a message from the Activity Stream and attach the file via the “sel ect document from library” link in the upload interface (Image 1), or a link to the document can be obtained fr om the action button in the library and sent (Image 3).
Files can also be attached to tasks, meetings, work reports and CRM elements.
This is an old post (from 2012) and Drive has been modified, please read this post now. You can't change the location of the file uploaded via Activity Stream now, but you can upload files to My Drive\Company Drive folders directly & share them within Activity Stream after.