Adding this line, simply removes the formatting you have added, by replacing the range with what it was originally. What you should have is
Code:
Dim p As Paragraph 'Declare your variables
Dim Thistext As String
Dim meetssomecondition As Boolean
For Each p In ActiveDocument.Paragraphs
meetssomecondition = False 'Set the boolean value to false for each paragraph0
Thistext = p.Range.Text 'Record the text content of the paragraph range
Debug.Print Thistext
If Left(Thistext, 5) = "Lorem" Then meetssomecondition = True 'add a condition relating to the text that will set the boolean value to True
If meetssomecondition = True Then 'If that condition is met set the paragraph range to bold font
p.Range.Font.Bold = True
End If
Next p