Hi,

Try the below code snippet as reference:

.........

Page

.........

<apex:page controller="sendEmail">

    <apex:messages />

    <apex:pageBlock title="Send an Email to Your {!account.name} Representatives">

        <p>Fill out the fields below to test how you might send an email to a user.</p>

        <apex:dataTable value="{!account.Contacts}" var="contact" border="1">

            <apex:column >

                <apex:facet name="header">Name</apex:facet>

                {!contact.Name}</apex:column>

            <apex:column >

                <apex:facet name="header">Email</apex:facet>

                {!contact.Email}</apex:column>

        </apex:dataTable>

        <apex:form ><br/><br/>

            <apex:outputLabel value="Subject" for="Subject"/>: <br/>    

            <apex:inputText value="{!subject}" id="Subject" maxlength="80"/>

            <br/><br/>

            <apex:outputLabel value="Body" for="Body"/>: <br/>    

            <apex:inputTextarea value="{!body}" id="Body" rows="10" cols="80"/>          

            <br/><br/>

            <apex:commandButton value="Send Email" action="{!send}"/>

        </apex:form>

    </apex:pageBlock>

    <apex:pageBlock title="Preview the Attachment for {!account.name}">

        <c:attachment />

    </apex:pageBlock></apex:page>

..............

Controller

..............

 public class sendEmail {

    public String subject {get; set;}

    public String body { get; set; }

    private final Account account;

    // Create a constructor that populates the Account object

    public sendEmail() {

        account = [SELECT Name,

                  (SELECT Contact.Name, Contact.Email FROM Account.Contacts)

                   FROM Account

                   WHERE Id = :ApexPages.currentPage().getParameters().get('id')];

    }

    public Account getAccount() {

        return account;

    }

    public PageReference send() {

        // Define the email

        Messaging.SingleEmailMessage email = new Messaging.SingleEmailMessage();

        // Reference the attachment page and pass in the account ID

        PageReference pdf =  Page.EmailAttachment;

         Blob b = pdf.getContent();

        System.debug('____________________________Pdf___________________________'+pdf);

        pdf.getParameters().put('id',(String)account.id);

        pdf.setRedirect(true);

        System.debug('____________________________Blob___________________________'+b);

        // Create the email attachment

        Messaging.EmailFileAttachment efa = new Messaging.EmailFileAttachment();

        efa.setFileName('attachment.pdf');

        efa.setBody(b);

        String addresses;

        if (account.Contacts[0].Email != null) {

            addresses = account.Contacts[0].Email;

            // Loop through the whole list of contacts and their emails

            for (Integer i = 1; i < account.Contacts.size(); i++) {

                if (account.Contacts[i].Email != null) {

                    addresses += ':' + account.Contacts[i].Email;

                }

            }

        }

        String[] toAddresses = addresses.split(':', 0);

        // Sets the paramaters of the email

        email.setSubject( subject );

        email.setToAddresses( toAddresses );

        email.setPlainTextBody( body );

        email.setFileAttachments(new Messaging.EmailFileAttachment[] {efa});// Sends the email

        Messaging.SendEmailResult [] r =

            Messaging.sendEmail(new Messaging.SingleEmailMessage[] {email});  

        return null;

    }

}

When you will run this code then first of all you will pass "Account Id" into URL.

Did this answer your question? If not, let me know what didn't work, or if so, please mark it solved.