First of all install Mail merge tool kit from 

Open word and select “Mailings” ribbon button

Click on the “Start Mail Merge” group:

Step 1

First, the output type of the document has to be specified. Since we’re merging a Word file to an E-mail message – select E-mail Messages and click Next.

Step 2

Select Use the current document, and click Next.

Step 3

With Use an existing list option selected, click Browse… and navigate to the Excel data-source on your computer. Microsoft Word will show the contents of the worksheet in a small window, where sheets and recipients can be specified.
Click Next.

Step 4

Now you can write the contents of the E-mail message, if started with a blank document, and also add merge fields for personalization, if they exist in the Excel worksheet (in this example, the ‘name’ field is used):

After doing so, click Next.

Step 5

This is, effectively, a proofreading stage – here you can verify that the merge fields are working and that the correct recipients are selected. Click Next when ready.

Step 6

Click the Mail Merge Toolkit button on the Wizard window (or the Merge & Send icon on the Word ribbon). Both Word Mail Mergeand Mail Merge Toolkit require the same steps to be done to configure the mailing, but Mail Merge Toolkit introduces lots of new features.

On the final window, specify the important fields, such as To (choose here the name of the worksheet column that holds the recipient e-mail information), Subject line (it can also be personalized!) and the mailing Format (for standard merging, choose HTML, Filtered), and any additional ones you require.
Note that you do not need to select “PDF, Attachment” as a mailing format if you wish to include .PDF files as attachments.

Clicking Ok means that you’ve successfully configured your mailing, and – after you specify the account to send from a folder to store the temporary copy of your Word document – Outlook should be able to send it in E-mail messages right away!