Feature Request
Brief title for your desired feature:
Make PDF one of the allowed formats for uploading as an attachement to a project.
How would you like the feature to work?
There are various formats allowed for attachments to projects but strangely the almost universal PDF format is not allowed.
Why is this feature important to you?
There are many things like datasheets, application notes, articles, specifications and copies of papers that are in PDF format which makes it possible for everyone to open and read them.
Brand new interactions and interfaces. 
Easy to use and quick to get started. 
I support the request for pdf attachments to project.
It helps to keep the design up to date by adding information that are helpful in understanding the desing, the rationale behind it and what changes were made and why.