So my use case is, when a BatchApex runs for every one hour, it inserts records on QNews custom object.
After Trigger fire every time when a record is inserted on QNews object and  sends an email with a PDF attachment.
I’m getting following error when Batch Apex runs, FATAL_ERROR|System.AsyncException: Future method cannot be called from a future or batch method: SendVFAsAttachment.sendVF(String, String, String, String, Id, String, String, String).

My ApexBatch:
global with sharing class ArticleBatch implements Database.Batchable<string>{
public Iterable<string> start(Database.BatchableContext bc)
    return new ArticleBatchIterable();  }

public void execute(Database.BatchableContext bc, List<string> scope){
    string articleTypeName = scope[0];    
    QNewsUpdateBatch batchClassObj = new QNewsUpdateBatch();
    batchClassObj.insertQnewsData(articleTypeName);
}
global void finish(Database.BatchableContext bc){
      //code that sends an email for execution of Batch    
}

My Trigger:
trigger Send_PDF_to_SharePointhelp on QNews__c (after insert, after update) {
    for(QNews__c qn: Trigger.new){
        string filename = qn.Article_Title__c+'_'+qn.Article_Version_Number__c+'.pdf';
        String emailbody='This attachment is the PDF copy of Article:  '+qn.Article_Title__c+' with version number '+qn.Article_Version_Number__c;   SendVFAsAttachment.sendVF('vijaku@vsp.com',qn.Data_Category__c,emailbody,UserInfo.getSessionId(),qn.Article_ID__c,qn.Article_Title__c,filename,qn.Article_Type__c); 
    }  
}

Future Method:
public class SendVFAsAttachment{
    @future(callout=true)
    public static void sendVF(String EmailIdCSV, String Subject,String body,String userSessionId, ID articleid,String ArticleTitle,String attachmentfilename,String ArticleType)
    {
        string newID = String.valueOf(articleid);
        String addr = 'https://vsp--kmbuild.cs10.my.salesforce.com/services/apexrest/sendPDFEmail';
        HttpRequest req = new HttpRequest();
        req.setEndpoint( addr );
        req.setMethod('POST');
        req.setHeader('Authorization', 'OAuth ' + userSessionId);
        req.setHeader('Content-Type','application/json');
        Map<String,String> postBody = new Map<String,String>();
        postBody.put('EmailIdCSV',EmailIdCSV);
        postBody.put('Subject',Subject);
        postBody.put('body',body);
        postBody.put('newID',newID);
        postBody.put('attachmentfilename',attachmentfilename);
        postBody.put('ArticleTitle',ArticleTitle);
        postBody.put('ArticleType',ArticleType);
        String reqBody = JSON.serialize(postBody);
        req.setBody(reqBody);
        Http http = new Http();
        HttpResponse response = http.send(req);
    }
}

Class to send email, exposed to REST API:
@RestResource(urlMapping='/sendPDFEmail/*')
Global class GETPDFContent{
     @HttpPost
    global static void sendEmail(String EmailIdCSV, String Subject, String body,string newID,string attachmentfilename,string ArticleTitle,string ArticleType) {
    List<String> EmailIds = EmailIdCSV.split(',');
        PageReference ref = Page.Multi_Topic_PDF;
        if(ArticleType=='Multi_Topic__kav'){
            ref = Page.Multi_Topic_PDF; 
          }
         if(ArticleType=='Additional_Benefits__kav'){
            ref = Page.AdditionalBenefits_PDF; 
          }
         if(ArticleType=='Core_Benefit__kav'){
            ref = Page.CoreBenefit_PDF; 
          }
         if(ArticleType=='Multi_Topic_Details__kav'){
            ref = Page.MultiTopicDetails_PDF; 
          }
         if(ArticleType=='Open_Enrollment__kav'){
            ref = Page.OpenEnrollment_PDF; 
          }
         if(ArticleType=='Single_Topic__kav'){
            ref = Page.SingleTopic_PDF; 
          }
            ref.getParameters().put('id',newID); 
            ref.setRedirect(true);
        Blob b = ref.getContentAsPDF();
        Messaging.SingleEmailMessage email = new Messaging.SingleEmailMessage();
        Messaging.EmailFileAttachment efa1 = new Messaging.EmailFileAttachment();
        efa1.setFileName(attachmentfilename);
        efa1.setBody(b);
        String addresses;
        email.setSubject( Subject );
        email.setToAddresses(EmailIds);
        email.setPlainTextBody(Body);
        email.setFileAttachments(new Messaging.EmailFileAttachment[] {efa1});
        Messaging.SendEmailResult [] r = Messaging.sendEmail(new Messaging.SingleEmailMessage[] {email});
    }
}