We currently utilize Office 365 with OneDrive and Sharepoint and have found it better when collaborating on files to include the link to the file versus inserting the file directly to the Wrike task. We have had issues with the files being slow to open and having too many methods of feedback.
You can 'upload' files using Sharepoint. When opening the file (it looks like an attachment) it will open the file on Sharepoint. We stopped using the link in the description.
I will warn with this method the PDF's in SharePoint default open into Wrike, not SharePoint. So, for example, if you are wanting to collaborate on a pdf document, it will default open into Wrike and all comments or edits made in Wrike will live there, not SharePoint. This is fine if everyone knows to look to Wrike for those items.
The other option would be to teach everyone to right click on the pdf file in Wrike, then choose Open in New Tab, that will open it into your browser/app instead of Wrike. I can only assume this is because SharePoint does not have a native PDF editor/viewer in their system for Wrike to connect to.