var ss=SpreadsheetApp.getActiveSpreadsheet();
var sheet = ss.getSheetByName('Sheet1'); //your sheet name
var data = sheet.getRange('A2:D2').getValues(); //your cell range
The data will now be in a 2-dimensional array: [[A2-value, B2-value, C2-value, D2-value]]
In my Doc templates, I use named fields. Like {firstName} {lastName} {phone#} {Email} for example.
Call your Doc, and replace the fields with the data:
var Doc = DocumentApp.openById(##YourDocId##); //if making a copy from a template, grab the new file's Id upon creation and save to a var. Then use that var here.
Doc.replaceText('{firstName}', data[0][0]);
Doc.replaceText('{lastName}', data[0][1]);
Doc.replaceText('{phone#}', data[0][2]);
Doc.replaceText('{Email}', data[0][3]);
This could be cleaned up a lot and simplified, but that should give you an idea of how to do it.