having the opportunity to upload a document for my account/ company/ the organization e.g. to have an overview of costs and other ressources

@T_Perschel Could you please share more details on what you are looking for? Do you mean you would like to attach a file at a specific organization? If so, just like what @Monish mentioned above, you can add attachments by clicking on the paper clip icon.

Or are you looking for a way to import other information (i.e. Costs of each task, etc) into Quire? If so, having Custom Fields is in our consideration for future improvements. When that's available in the future, this might be possible then. Thanks!

If I recall correctly, you can add attachments under 6MB directly to Quire using the attachment icon (the paper clip)