How to get DocMan Version

gistfile1.php

function get_docman_ver( &$majDMver, &$minDMver) {
	$maj = $min = 0;
	if ( file_exists(JPATH_BASE . '/administrator/components/com_docman/version.php') ) {
		include_once( JPATH_BASE . '/administrator/components/com_docman/version.php' );
		sscanf( ComDocmanVersion::getVersion(), "%i.%i", $maj, $min);
	} else {
		if ( file_exists(JPATH_BASE . '/administrator/components/com_docman/includes/defines.php') ) {
			include_once( JPATH_BASE . '/administrator/components/com_docman/includes/defines.php' );
			sscanf( _DM_VERSION, "%i.%i", $maj, $min);
		} else // Unknown DocMan or not installed
			return FALSE;
	}
	$majDMver = $maj;
	$minDMver = $min;
	return TRUE;
}

if(JComponentHelper::getComponent('com_docman', true))
{
    if(defined('_DM_VERSION')) {
        $version = _DM_VERSION;
    } else {
        $version = ComDocmanVersion::VERSION;
    }
}

To check the version against a pre-defined version in your code you can use http://php.net/manual/en/function.version-compare.php

Example

if(version_compare($version, '2.0.0') >= 0) {
   //You are using DOCman 2.0+
}