diff --git a/extensions/mongo/file/ActiveQuery.php b/extensions/mongo/file/ActiveQuery.php
index 005e4ce..91661d6 100644
--- a/extensions/mongo/file/ActiveQuery.php
+++ b/extensions/mongo/file/ActiveQuery.php
@@ -11,7 +11,23 @@ use yii\db\ActiveQueryInterface;
 use yii\db\ActiveQueryTrait;
 
 /**
- * Class ActiveQuery
+ * ActiveQuery represents a Mongo query associated with an file Active Record class.
+ *
+ * ActiveQuery instances are usually created by [[ActiveRecord::find()]].
+ *
+ * Because ActiveQuery extends from [[Query]], one can use query methods, such as [[where()]],
+ * [[orderBy()]] to customize the query options.
+ *
+ * ActiveQuery also provides the following additional query options:
+ *
+ * - [[with()]]: list of relations that this query should be performed with.
+ * - [[asArray()]]: whether to return each record as an array.
+ *
+ * These options can be configured using methods of the same name. For example:
+ *
+ * ~~~
+ * $images = ImageFile::find()->with('tags')->asArray()->all();
+ * ~~~
  *
  * @author Paul Klimov <klimov.paul@gmail.com>
  * @since 2.0
diff --git a/extensions/mongo/file/ActiveRecord.php b/extensions/mongo/file/ActiveRecord.php
index 1bb2f55..c7ca752 100644
--- a/extensions/mongo/file/ActiveRecord.php
+++ b/extensions/mongo/file/ActiveRecord.php
@@ -14,16 +14,47 @@ use yii\web\UploadedFile;
 /**
  * ActiveRecord is the base class for classes representing Mongo GridFS files in terms of objects.
  *
+ * To specify source file use the [[file]] attribute. It can be specified in one of the following ways:
+ *  - string - full name of the file, which content should be stored in GridFS
+ *  - \yii\web\UploadedFile - uploaded file instance, which content should be stored in GridFS
+ *
+ * For example:
+ *
+ * ~~~
+ * $record = new ImageFile();
+ * $record->file = '/path/to/some/file.jpg';
+ * $record->save();
+ * ~~~
+ *
+ * You can also specify file content via [[newFileContent]] attribute:
+ *
+ * ~~~
+ * $record = new ImageFile();
+ * $record->newFileContent = 'New file content';
+ * $record->save();
+ * ~~~
+ *
+ * Note: [[newFileContent]] always takes precedence over [[file]].
+ *
+ * @property \MongoId|string $_id primary key.
+ * @property string $filename name of stored file.
+ * @property \MongoDate $uploadDate file upload date.
+ * @property integer $length file size.
+ * @property integer $chunkSize file chunk size.
+ * @property string $md5 file md5 hash.
+ * @property \MongoGridFSFile|\yii\web\UploadedFile|string $file associated file.
+ * @property string $newFileContent new file content.
+ *
  * @author Paul Klimov <klimov.paul@gmail.com>
  * @since 2.0
  */
-class ActiveRecord extends \yii\mongo\ActiveRecord
+abstract class ActiveRecord extends \yii\mongo\ActiveRecord
 {
 	/**
 	 * Creates an [[ActiveQuery]] instance.
 	 * This method is called by [[find()]] to start a "find" command.
-	 * You may override this method to return a customized query (e.g. `CustomerQuery` specified
-	 * written for querying `Customer` purpose.)
+	 * You may override this method to return a customized query (e.g. `ImageFileQuery` specified
+	 * written for querying `ImageFile` purpose.)
 	 * @return ActiveQuery the newly created [[ActiveQuery]] instance.
 	 */
 	public static function createQuery()
@@ -55,7 +86,18 @@ class ActiveRecord extends \yii\mongo\ActiveRecord
 	/**
 	 * Returns the list of all attribute names of the model.
 	 * This method could be overridden by child classes to define available attributes.
-	 * Note: primary key attribute "_id" should be always present in returned array.
+	 * Note: all attributes defined in base Active Record class should be always present
+	 * in returned array.
+	 * For example:
+	 * ~~~
+	 * public function attributes()
+	 * {
+	 *     return array_merge(
+	 *         parent::attributes(),
+	 *         ['tags', 'status']
+	 *     );
+	 * }
+	 * ~~~
 	 * @return array list of attribute names.
 	 */
 	public function attributes()
diff --git a/extensions/mongo/file/Collection.php b/extensions/mongo/file/Collection.php
index fbe65be..b3c722b 100644
--- a/extensions/mongo/file/Collection.php
+++ b/extensions/mongo/file/Collection.php
@@ -13,6 +13,10 @@ use Yii;
 /**
  * Collection represents the Mongo GridFS collection information.
  *
+ * A file collection object is usually created by calling [[Database::getFileCollection()]] or [[Connection::getFileCollection()]].
+ *
+ * File collection inherits all interface from regular [[\yii\mongo\Collection]], adding methods to store files.
+ *
  * @property \yii\mongo\Collection $chunkCollection file chunks Mongo collection. This property is read-only.
  * @method \MongoGridFSCursor find() returns a cursor for the search results.
  *
@@ -61,6 +65,8 @@ class Collection extends \yii\mongo\Collection
 	}
 
 	/**
+	 * Creates new file in GridFS collection from given local filesystem file.
+	 * Additional attributes can be added file document using $metadata.
 	 * @param string $filename name of the file to store.
 	 * @param array $metadata other metadata fields to include in the file document.
 	 * @param array $options list of options in format: optionName => optionValue
@@ -85,6 +91,8 @@ class Collection extends \yii\mongo\Collection
 	}
 
 	/**
+	 * Creates new file in GridFS collection with specified content.
+	 * Additional attributes can be added file document using $metadata.
 	 * @param string $bytes string of bytes to store.
 	 * @param array $metadata other metadata fields to include in the file document.
 	 * @param array $options list of options in format: optionName => optionValue
@@ -109,6 +117,8 @@ class Collection extends \yii\mongo\Collection
 	}
 
 	/**
+	 * Creates new file in GridFS collection from uploaded file.
+	 * Additional attributes can be added file document using $metadata.
 	 * @param string $name name of the uploaded file to store. This should correspond to
 	 * the file field's name attribute in the HTML form.
 	 * @param array $metadata other metadata fields to include in the file document.
diff --git a/extensions/mongo/file/Query.php b/extensions/mongo/file/Query.php
index 4c1e5ff..c15d4f1 100644
--- a/extensions/mongo/file/Query.php
+++ b/extensions/mongo/file/Query.php
@@ -12,7 +12,11 @@ use yii\helpers\Json;
 use yii\mongo\Exception;
 
 /**
- * Class Query
+ * Query represents Mongo "find" operation for GridFS collection.
+ *
+ * Query behaves exactly as regular [[\yii\mongo\Query]].
+ * Found files will be represented as arrays of file document attributes with
+ * additional 'file' key, which stores [[\MongoGridFSFile]] instance.
  *
  * @author Paul Klimov <klimov.paul@gmail.com>
  * @since 2.0