How to add a link to off line Html docs located on a sharedrive ?

Hi tgroppi 

I don't have an on-premises SP environment to test this in, but you might be able to make this work by creating .url files in your SP document library.

Create a text file with a .url extension and content similar to:

[InternetShortcut]
"URL=file:////fileServerName/shareName/index.htm"

Upload the .url file to your document library. I can't do this on SharePoint online since .url files are blocked, but you should be able to override this for on-premises installations if needed. But check doing so is compatible with your security policy.

An alternative might be to add links in your site header to file:////fileServerName/shareName/index.htm.