As you don't state how you want to use the result, I just created a list of booleans
XNamespace xns = "http://www.somesite.com/";
XDocument xdInput = XDocument.Load(@"C:\Temp\input.xml");
XElement xeWP = xdInput.Root.Element(xns + "p");
var existList = from el in xeWP.Elements(xns + "r")
select (el.Element(xns + "tab") != null && el.Element(xns + "t") != null);
To make it work I enclosed your XML data in a new root element
<root xmlns:w="http://www.somesite.com/">
<w:p w:rsidR="00DC605B" w:rsidP="00A60D85" w:rsidRDefault="009A6F33">
...
</w:p>
</root>
This snippet just prints out the result:
for (int i = 0; i < existList.Count(); i++)
Console.WriteLine("Item {0} : {1}", i + 1, existList.ElementAt(i));