SRTM(Shuttle Radar Topography Mission) is a mission that obtained digital elevation models on a global scale. The measurement results are published on the United States Geological Survey's website.
GPX Binder can calculate elevation of point by installing correct SRTM files.

SRTM files are provided as mesh tiles, each covering one degree of latitude and one degree of longitude. The size of each file is about 3MB, but in total size is over 15GB.
So GPX Binder does not contain SRTM files. If you want to use, you need to download and install them by yourself.

Select points on the Map and Select "Get Elevation of Selected Point" from the action menu under the point list. If there are correct SRTM tiles, the elevation will be automatically apply to the points. If not, an alert will be shown like this:
At the first line of this alert shows the name of required tiles (In this case, the name of tile is "N36E138"). Note them, and close the alert.

You can download SRTM Files from the United States Geological Survey's website. Download files named (Tile Name) +.hgt.zip and unzip them on your desktop.

SRTM-3 version2.1（old version）
http://dds.cr.usgs.gov/srtm/version2_1/SRTM3/

SRTM-3 version3（new version. a warning will be shown when you access this server. You should download files on this server on your own responsibility.）
https://e4ftl01.cr.usgs.gov/MEASURES/SRTMGL1.003/2000.02.11/

Note：There are three kind of SRTM files. SRTM-30 (900m mesh) , SRTM-3 (90m mesh) and SRTM-1 (30m mesh). GPX Binder is Currently be able to use SRTM-3 only.

Show the Preferences Panel the GPX Binder (⌘ - ,), and click SRTM tab. Click button and select .hgt file you have unzipped. You can also drag and drop files into the list directory.

Confirm SRTM files are shown on the list, and close the panel.

Select points on the Map and Select "Get Elevation of Selected Point" from the action menu under the point list. GPX Binder calculates elevations and applies them to the points.