When i try to export map to jpg file in ArcGIS DEsktop 10.3, the "write world file" is blocked.
How can i solve this problem?
This option is only available in Data View.
If you are in Layout View then you will not be able to Write a World File.
This software behaviour is unchanged in ArcGIS 10.4 for Desktop Pre-release.
For it to be enhanced I suggest you submit an ArcGIS Idea. I was surprised not to find one when I looked just now. If you do submit one then I suggest targeting ArcGIS Pro (where this functionality appears to be the same as ArcMap's) rather than ArcMap because I think it will have a better chance of being implemented there.
I am assuming that data frame boundaries in layout view coincide with page.
This can be done manually, because you truly need just 3 values to create world file: cell size and coordinates of upper left corner of exported image.
Export layout to raster file and note it's height in pixels, e.g. 842. To find 3 magic numbers activate python window from layout view and type:
mxd = arcpy.mapping.MapDocument("CURRENT") df = arcpy.mapping.ListDataFrames(mxd) ext=df.extent
This gives you access to data frame extent. Following 3 lines will give you numbers:
ext.height/842 ext.XMin ext.YMax
to be placed in relevant lines inside world file.