Is it possible to convert in QGIS a GRD file (that was created in MapInfo) into an ASC file (that can be imported into SAGA)?
Is it possible to "extract by mask" a section of a GRD file in an other format than GeoTiff in QGIS?
Just try to add it to QGis as a new raster. If your file-format is in this list and supported by GDAL, then it will probably also be accessible in QGis.
You can "extract by mask" with the Gdal clipper tool. See this blog post for an example.