Yes!! There is a solution:
If you open the SharePoint pdf document list, open your web browser developer tools, Choose the pdf from sharepoint list, Right click, choose the "download" button from sharepoint list. now you will find a uniqueID from developer tools under Network, go to find the download.aspx?UniqueID:

Copy this url to PowerApps Button Onselect

It will download this file directly.
Hope this helps and works for you!