A problem with searching inside a Word document XML file is that the text can be split into elements at any character. It will certainly be split if formatting is different, for example as in Hello World. But it can be split at any point and that is valid in OOXML. So you will end up dealing with XML like this even if formatting does not change in the middle of the phrase!
<w:p w:rsidR="00C07F31" w:rsidRDefault="003F6D7A">
<w:r w:rsidRPr="003F6D7A">
<w:rPr>
<w:b />
</w:rPr>
<w:t>Hello</w:t>
</w:r>
<w:r>
<w:t xml:space="preserve">World.</w:t>
</w:r>
</w:p>
You can of course load it into an XML DOM tree (not sure what this will be in Python) and ask to get text only as a string, but you could end up with many other "dead ends" just because the OOXML spec is around 6000 pages long and MS Word can write lots of "stuff" you don't expect. So you could end up writing your own document processing library.
Or you can try using Aspose.Words.
It is available as .NET and Java products. Both can be used from Python. One via COM Interop another via JPype. See Aspose.Words Programmers Guide, Utilize Aspose.Words in Other Programming Languages (sorry I can't post a second link, stackoverflow does not let me yet).