To open an ASN.1 schema file for editing, select the Open Schema... option from the File menu. This will bring up a dialog box for selecting the file.

In the file-type dropdown, select "ASN.1 Schemas (*.asn *.asn1)" and select a file. If the file to be opened has a nonstandard file extension, selecting "All files (*)" will allow the file type (ASN.1 schema, in this case) to be chosen manually.

Once the schema file is opened, it is displayed in the Editor Tab in the Document View window. From there, it can be viewed or edited. The schema can also be validated by using the Validate schema option in the Tools menu. The Validate Schema toolbar button can also be used to do this:

If validation is successful, the schema will be displayed in the ASN.1 Browser Tab as well as the Editor. It will also be shown in the Tree View under the ASN.1 Schema Tab thus allowing for easy navigation to all items within the schema.