Using Geotiff USGS SRTM DEM file

Could you help about how to use in Mike 11 or Mike Hydro, a DEM of a Geotiff SRTM file withou need to use ArcGIS ?
Or, how to convert Geotiff SRTM DEM file to an ESRI ASCII like file, without using ArcGIS  ?

If you had Arcgis softwareyou could follow the following link :
http://faq.dhigroup.com/default.asp?module=Other+tools&ID=368
But I think you can use some free Gis software like Qgis
You can download it from this link:
https://www.qgis.org/en/site/forusers/download.html

I think by reading the following link you could get familiar with to convert raster to Ascii files.

http://gis.stackexchange.com/questions/77306/how-to-convert-raster-to-point-in-qgis


cheers.