CustomConversion.vfp

<apex:page standardController="Lead" extensions="ConvertExt" sidebar="false">
    <apex:pageBlock title="Custom Lead Conversion" tabStyle="Lead" id="LeadBlock">
        <apex:pageBlockSection title="Lead Details">
            <apex:outputField value="{!lead.LastName}"/>
            <apex:outputField value="{!lead.OwnerId}"/>
            <apex:outputField value="{!lead.Company}"/>
            <apex:outputField value="{!lead.Id}"/>
            <apex:outputField value="{!lead.Status}" id="leadStatus"/>
        </apex:pageBlockSection>
        <apex:form >
            <div align="center" draggable="false">
               <apex:commandButton disabled="{! if(IsConverted , true, false)}" value="Start Conversion" action="{!convertLead}" /> 
            </div>            
        </apex:form>        
    </apex:pageBlock>   
</apex:page>