public void Modify( 
   FeatureClassDescription featureClassDescription
)

      
// Adding following fields to the 'Parcels' FeatureClass
// Global ID
// Parcel_ID
// Tax_Code
// Parcel_Address
      

// The FeatureClass to add fields
string featureClassName = "Parcels";

FeatureClassDefinition originalFeatureClassDefinition = geodatabase.GetDefinition<FeatureClassDefinition>(featureClassName);
FeatureClassDescription originalFeatureClassDescription = new FeatureClassDescription(originalFeatureClassDefinition);

// The four new fields to add on the 'Parcels' FeatureClass
FieldDescription globalIdField = FieldDescription.CreateGlobalIDField();
FieldDescription parcelIdDescription = new FieldDescription("Parcel_ID", FieldType.GUID);
FieldDescription taxCodeDescription = FieldDescription.CreateIntegerField("Tax_Code");
FieldDescription addressDescription = FieldDescription.CreateStringField("Parcel_Address", 150);

List<FieldDescription> fieldsToAdd = new List<FieldDescription> { globalIdField, parcelIdDescription, 
  taxCodeDescription, addressDescription };

// Add new fields on the new FieldDescription list
List<FieldDescription> modifiedFieldDescriptions = new List<FieldDescription>(originalFeatureClassDescription.FieldDescriptions);
modifiedFieldDescriptions.AddRange(fieldsToAdd);

// The new FeatureClassDescription with additional fields
FeatureClassDescription modifiedFeatureClassDescription = new FeatureClassDescription(originalFeatureClassDescription.Name,
  modifiedFieldDescriptions, originalFeatureClassDescription.ShapeDescription);

SchemaBuilder schemaBuilder = new SchemaBuilder(geodatabase);

// Update the 'Parcels' FeatureClass with newly added fields
schemaBuilder.Modify(modifiedFeatureClassDescription);
bool modifyStatus = schemaBuilder.Build();

if (!modifyStatus)
{
  IReadOnlyList<string> errors = schemaBuilder.ErrorMessages;
}

// Removing all fields from 'Parcels' table except following 
// Tax_Code
// Parcel_Address
      

// The table to remove fields
string tableName = "Parcels";

TableDefinition tableDefinition = geodatabase.GetDefinition<TableDefinition>(tableName);
IReadOnlyList<Field> fields = tableDefinition.GetFields();

// Existing fields from 'Parcels' table
Field taxCodeField = fields.First(f => f.Name.Equals("Tax_Code"));
Field parcelAddressField = fields.First(f => f.Name.Equals("Parcel_Address"));

FieldDescription taxFieldDescription = new FieldDescription(taxCodeField);
FieldDescription parcelAddressFieldDescription = new FieldDescription(parcelAddressField);
      
// Fields to retain in modified table
List<FieldDescription> fieldsToBeRetained =new List<FieldDescription>()
{
  taxFieldDescription, parcelAddressFieldDescription 
};

// New description of the 'Parcels' table with the 'Tax_Code' and 'Parcel_Address' fields
TableDescription modifiedTableDescription = new TableDescription(tableName, fieldsToBeRetained);

SchemaBuilder schemaBuilder = new SchemaBuilder(geodatabase);

// Remove all fields except the 'Tax_Code' and 'Parcel_Address' fields
schemaBuilder.Modify(modifiedTableDescription);
schemaBuilder.Build();

// Adding a field,'PipeType', which uses the coded value domain to the 'Pipes' FeatureClass

//The FeatureClass to add field
string featureClassName = "Pipes";

SchemaBuilder schemaBuilder = new SchemaBuilder(geodatabase);

// Create a CodedValueDomain description for water pipes
CodedValueDomainDescription pipeDomainDescription = new CodedValueDomainDescription("WaterPipeTypes", FieldType.String,
  new SortedList<object, string> { { "Copper", "C_1" },
    { "Steel", "S_2" } })
{
  SplitPolicy = SplitPolicy.Duplicate,
  MergePolicy = MergePolicy.DefaultValue
};

// Create a coded value domain token
CodedValueDomainToken codedValueDomainToken = schemaBuilder.Create(pipeDomainDescription);

// Create a new description from domain token
CodedValueDomainDescription codedValueDomainDescription = new CodedValueDomainDescription(codedValueDomainToken);

// Create a field named as 'PipeType' using a domain description
FieldDescription domainFieldDescription = new FieldDescription("PipeType", FieldType.String)
{ DomainDescription = codedValueDomainDescription };

//Retrieve existing information for 'Pipes' FeatureClass
FeatureClassDefinition originalFeatureClassDefinition = geodatabase.GetDefinition<FeatureClassDefinition>(featureClassName);
FeatureClassDescription originalFeatureClassDescription = new FeatureClassDescription(originalFeatureClassDefinition);

// Add domain field on existing fields
List<FieldDescription> modifiedFieldDescriptions = new List<FieldDescription>(originalFeatureClassDescription.FieldDescriptions) { domainFieldDescription };

// Create a new description with updated fields for 'Pipes' FeatureClass 
FeatureClassDescription featureClassDescription = new FeatureClassDescription(originalFeatureClassDescription.Name, modifiedFieldDescriptions,
  originalFeatureClassDescription.ShapeDescription);

// Update the 'Pipes' FeatureClass with domain field
schemaBuilder.Modify(featureClassDescription);

// Build status
bool buildStatus = schemaBuilder.Build();

// Build errors
if (!buildStatus)
{
  IReadOnlyList<string> errors = schemaBuilder.ErrorMessages;
}