Short answer is yes, it is possible. However, the way to achieve this will depend on some factors:
1.) Are you using CRM online or On Premises? If you are running on Premises your HTML web resource can point to some .net solution that runs in the same pool as the crm.
2.) What type of file is this? Text files can easily be rendered using JavaScript and with the correct settings it can be downloaded. More complicated types of files will be more complicated to implement.
3.) What tools and software are you planning on using? If you are familiar with Silverlight you can produce very powerful plugins.
Please give more detail on exactly what you want to achieve. Maybe also some screenshots if possible.
Christo Vermeulen