Since July 25th, 2018, the National Archives have put online the documents of the Civil registers of Luxembourg. Click on the + in front of the said folder to open the list of municipalities, then on the + in front of the municipality of your choice to open the folders with records of this municipality. Double-click on the folder of your choice and the image of the first page of this folder is displayed. Below in the Files (Fichiers) section, you click in the document ending with .pdf.
This PDF document now opens in a 2nd window. After downloading, you can save this document on your computer with a right-click (Save as ...)