Search Engine Of Non-exact Word Using Userform

I have a userform for the user to use a search engine on what he needs. The following code I have written it, but it is only good if he writes exact wording of the document name. How can I twist the code to make the search look for approximate words,

The search engine will try to look in for all the titles on "Result" worksheet and copy/past it to a new sheet called "search". so when the user types in the userform "specification" for instance, it will look all titles (Specifications, specification, spec, brown color spec) that has this word in the "Result" sheet and then it will copy/paste it in the Search Sheet.

Code:
Private Sub ok_1_Click()
Dim sht As Worksheet
Set sht = Worksheets("Result")
'if no name selected
If Trim(Me.Document_box.Value) = "" Then
MsgBox "Please write a document name."

[Code] ......