New mouldings on either side of the window will likely be required. Doors tend to be mounted flush with the inside face for aesthetics and ease of operation. Once the window is installed, check that it opens and closes easily, locks tightly, and is well-sealed. If condensation occurs between panes of sealed units, the seal is faulty and the unit should be replaced under warranty. Different things are covered by different kinds of warranties.
Shorter periods suggest the manufacturer has used less effective sealing methods.
If condensation, frosting, fogging, or discolouration appear between the layers of glazing within the warranty period, the manufacturer will replace the sealed unit. The rest of the unit is usually under warranty for performance under normal operating conditions. The minimum to settle for is one year, parts and labour. Make sure the installer's workmanship is also covered by warranty. If the installer breaks the seal of a window, for example, that window would have to be replaced.