You cannot download Microsoft Flight Simulator X.
You cannot download Microsoft Flight Simulator 2004, you have to buy it.
Yes, you can download add-ons for Microsoft Flight Simulator 2004.
The download for the Antonov 225 for Microsoft Flight Simulator X is is in the link below this question.
There is no need to buy Microsoft Flight Simulator X: Deluxe Edition as Microsoft Flight Simulator X: Acceleration contains everything from Microsoft Flight Simulator X: Deluxe Edition and more.
I have found a download for the Embraer 135 for Microsoft Flight Simulator X. I have put the link to the download below this question. To download you must register with the website but registration is free.
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No, Microsoft Flight Simulator 2004 add-on aircraft cannot be transferred to Microsoft Flight Simulator X.
No, you cannot use the add-ons for Microsoft Flight Simulator 98 in Microsoft Flight Simulator X.
Flight Simulator X is by Microsoft, the full name is Microsoft Flight Simulator X.
Microsoft Flight Simulator X: 18 Microsoft Flight Simulator X: Deluxe Edition: 22 Microsoft Flight Simulator X: Acceleration (add-on): 25 Microsoft Flight Simulator X: Gold Edition: 25
Microsoft Flight Simulator was created in 1982.