In order to upload documents and enable them for download you must first have the presenter role.
By default the first Moderator to enter the BigBlueButton session is allocated presenter role capabilities; if you are a viewer you will need to request presenter status from the moderator.
When a user has the presenter role, the presenter icon will appear over their avatar in the users list.
Next be sure your documents are within the size restrictions and are an accepted format.
Maximum size is 30 MB or 150 pages per document; you can upload multiple documents into the BigBlueButton as long as they are under the size restrictions.
BigBlueButton will accept Office documents ( .doc .docx .pptx), text documents (.txt), images (.png ,.jpg) and Adobe Acrobat documents (.pdf); we recommend converting documents to .pdf prior to uploading for best results.
Select the Actions menu  in the lower left hand corner of the presentation window, then choose Upload a Presentation .
The BigBlueButton presentation uploader will appear. The uploader allows you to drag and drop  files into the uploader or browse for files  on your OS.
When uploading multiple files at once, be sure to set the file you'd like to be displayed by default, then check the green circle to the right of the document.
Once you have selected your chosen file(s) for upload, press start to convert and upload the files.
Depending on the size of your document it may take several moments for it to convert and finally upload to the meeting.
Enabling for Download
Any presenter uploading a document can enable it for download by viewers of the live conference at any time.
To enable, select the enable download icon located to the right of the document.
The icon will change to green to indicate the document selected can be downloaded by viewers.
What Viewers See
Viewers will be able to download the enabled documents via the file download icon in the bottom left of their screens.