I am using the same controller. I am still not able to fix the issue.

public class ControllerClass {
	public String currentPageId{get;set;}
	public List<orderWrapper> orderListWrapper{get;set;}
	public Order__c orderObj{get;set;}
    public String parId{get;set;}
    public List<Order__c> selectedOrders{get;set;}
    public List<MultiOrderWrapperClass> multiOrderList{get;set;}
    
	public ControllerClass(){
	currentPageId = ApexPages.currentPage().getParameters().get('id');
	orderListWrapper = new List<orderWrapper>();
    selectedOrders = new List<Order__c>();
    multiOrderList = new List<MultiOrderWrapperClass>();
    } 
	
	public List<orderWrapper> getOrders(){
        for(Order__c o : [Select Name From Order where *somecondition*])
                orderListWrapper.add(new orderWrapper(o));
        return orderListWrapper;
	}
	public PageReference getSelected(){
        selectedOrders.clear();    
        for(OrderWrapper ordWrapper : orderListWrapper)
        if(ordWrapper.selected == true)
        selectedOrders.add(ordWrapper.ord);
        return null;
	}
	
public PageReference init(){
		multiOrderList = new List<MultiOrderWrapperClass>();
        Order__c orderObj = [Select Name from Order__c where id=: currentPageId];
        List<Id> selectedOrderIds = new List<Id>();
        for(Integer i=0; i<selectedOrders.size();i++ ){selectedOrderIds.add(selectedOrders[i].id);}
        for(Order obj : [Select Name from Order where id IN : selectedOrderIds]){
									
        		MultiOrderWrapperClass mOrderObj = new MultiOrderWrapperClass(obj);
            	multiOrderList.add(mOrderObj);
        }
    
        PageReference pdf = Page.SecondVFPage;
        pdf.getParameters().put('id',currentPageId);
		Datetime temp = Datetime.newInstance(datetime.now().year(), datetime.now().month(),datetime.now().day());
        Attachment attach = new Attachment();
        blob body;
       try
        {
            body = pdf.getcontent();
        }
        catch (visualforceexception e)
        {
            body = blob.valueof('some text');    // This is used to pass unit test criteria
        }
       attach.body = body;
        attach.name = 'Name'; 
        attach.isprivate = false;
        attach.parentid = currentPageId;
        insert attach;
        return new PageReference('/'+currentPageId);
        
    
	}
	public PageReference cancel(){
	return new PageReference('/'+currentPageId);

	}
	public class OrderWrapper{
		public Order__c ord{get; set;}
		public Boolean selected {get; set;}
		public orderWrapper(Order o){
            ord = o;
            selected = false;
		}
	}
	public class MultiOrderWrapperClass{
		public String name{get;set;}
		public MultiOrderWrapperClass(Order Obj){
		this.name = Obj.Name;
		}
	}
}



 



First VF Page
<apex:page controller="Creative_MultipleOrderLine" sidebar="false"> 
	<apex:form >
		<apex:pageBlock title="Parent : {!parId}">
 			<apex:pageBlockButtons >
    			<apex:commandButton value="Generate Order" action="{!init}"/>
    			<apex:commandButton value="Cancel" action="{!cancel}"/>
 			</apex:pageBlockButtons>
 			<apex:pageBlockSection title="Related Order List">
 			
 			 
 				<apex:dataTable value="{!orders}" var="o" columnswidth="50px,50px" cellpadding="4" border="1">
 				<apex:column >
 				<apex:facet name="header">
 				<!--<apex:inputCheckbox onclick="{!selectedOrders}">
 					  <apex:actionSupport event="onclick" action="{!getSelected}" onsubmit="checkAll(this)" rerender="Selected_ORD"/>
				</apex:inputCheckbox>-->
				</apex:facet>
			 	<apex:inputCheckbox value="{!o.selected}" id="checkedone">
					  <apex:actionSupport event="onclick" action="{!getSelected}" rerender="Selected_ORD"/>
				</apex:inputCheckbox>
				</apex:column>
				<apex:column headervalue="Order ID" value="{!o.ord.Name}" />
				</apex:dataTable>
			</apex:pageBlockSection>
			<apex:pageBlockSection Title="Selected Order List" id="Selected_ORD">
			<apex:dataTable value="{!SelectedOrders}" var="s" columnswidth="50px,50px" cellpadding="4" border="1">
			<apex:column headervalue="Order ID" value="{!s.Name}" />
			</apex:dataTable> 
			</apex:pageBlockSection>
			
		</apex:pageBlock>
	</apex:form>
</apex:page>

SecondVF Page
<apex:page controller="Creative_MultipleOrderLine" showheader="false" renderas="pdf"> 
View {!multiOrderList} View
</apex:page