Visit the project in which you want to upload a document and do the following:

1. Click on document to the left in the project view

2. Click on the gray icon with a plus sign, located at the top right of the page

3. Name the document and upload it from your computer

4. Click on save 

TIP!: The file format you can upload are: JPG, PNG, PDF, DOC, DOCX, XLS, XLSX