Could someone tell me if it’s possible, when I double click on a document in a view (client not web), to open the document in a small (pop-up) window?
Subject: Yes, it’s possible …
I did the trick this way :
in the QuerydocumentOpen event of the view
set the Continue parameter to false
retreive the clicked document (NotesUIView.CaretNotesID) and the underlying back end document (NotesDatabase.GetDocumentByID)
if doc is the retreived NotesDocument then use : NotesUIWorkspace.dialogbox(formname, , title, doc , …)
Subject: Thanks…it works for me too 
Needed a similar function, and found part of my answer here. Please find my code attached :-)It opens the currently selected document in a pop-up window, saves it when ‘OK’ is clicked, otherwise exits. If saved, the current view is refreshed.
Sub Queryopendocument(Source As Notesuiview, Continue As Variant)
Continue = False
Dim NotesUIWorkspace As New NotesUIWorkspace
Dim db As NotesDatabase
Dim doc As NotesDocument
Dim s As New NotesSession
Set db = s.CurrentDatabase
Set doc = db.GetDocumentByID(Source.CaretNoteID)
If Not NotesUIWorkspace.DialogBox("YOUR_FORM_HERE", True, True, False, False, False, False, "WINDOW_TITLE_HERE", doc) Then Exit Sub
Call doc.Save(True, False)
Call notesUIWorkspace.ViewRefresh
End Sub