Script for saving/sorting/sending emails based on their subject
Readability


Proper indentation is important for readability. Everything inside of Sub...End Sub should be indented one tab (or four spaces). Else If statements should line up with their corresponding If statements. For example:

Public Sub foo
    dim variable as boolean
    If variable Then
        'do something
    Else 
        'do something different
    End If
End Sub

Variable and routine names are overly abbreviated. We're no longer in the bad ol' days when the length of variable names were limited. Instead of attName, try attachmentName. Apply this to all of your variable names and Mr. Maintainer will thank you.
As a matter of opinion, Sub and Function names should be PascalCase. Instead of saveattachtodisk, try SaveAttachmentToDisk. I do like that you're following the verb-noun naming schema for them though. You did a good job there.
Back to over abbreviation. There are single letter parameter names. They tell me nothing about what I'm supposed to pass into them.


Functionality


What happens if "C:\Users\USER\Desktop\Staging" doesn't exist on the client machine? The code crashes. Adding some error handling in will help, but the routine should also either let the user pick a folder, or build the directory itself. It's looks like it's a temporary structure, so I recommend the latter. 
Let's talk about this section for a minute.

If whatIs = "PDF" Then
    objAtt.SaveAsFile saveFolder &amp; "\" &amp; UCase(saveName) &amp; ".pdf"
ElseIf whatIs = "DOC" Then
    objAtt.SaveAsFile saveFolder &amp; "\" &amp; "DOC 14-" &amp; stripNums(saveName) &amp; ".pdf"
    emailAttach = saveFolder + "\" + "DOC 14-" + stripNums(saveName) + ".pdf"
    attName = stripNums(saveName)
    sendDOC emailAttach, attName
ElseIf whatIs = "other" Then
    objAtt.SaveAsFile saveFolder &amp; "\" &amp; saveName &amp; ".pdf"
End If



This works great for now, but what happens when I want to expand it to include other document types? I'm thinking a DocType enum could go a long way toward making it easier to extend, as well as improve readability.

Public Enum DocType
    PDF
    DOC
End Enum

Select Case whatIs
    Case PDF
        objAtt.SaveAsFile saveFolder &amp; "\" &amp; UCase(saveName) &amp; ".pdf"
    Case DOC
        objAtt.SaveAsFile saveFolder &amp; "\" &amp; "DOC 14-" &amp; stripNums(saveName) &amp; ".pdf"
        emailAttach = saveFolder + "\" + "DOC 14-" + stripNums(saveName) + ".pdf"
        attName = stripNums(saveName)
        sendDOC emailAttach, attName
    Case Else
        objAtt.SaveAsFile saveFolder &amp; "\" &amp; saveName &amp; ".pdf"
End Case



The "Doc 14-" string show up a lot. Store it in a constant at the module scope.
saveFolder should be a constant at the procedure scope. If it doesn't change, declare it as a constant so Mr. Maintainer doesn't try to assign it a new value at runtime in the future.
You can break out of the for loop in isPDF() as soon as it finds the value it's looking for. There's also no reason for the returnValue variable to exist. Just assign the function value directly. Booleans are implicitly false upon creation, so isPDF() could look more like this.

'Checks to see if document is PDF type docement
Function isPDF(s As String) As Boolean
    For i = 1 To Len(s)
        If Mid(s, i, 2) = "1f" Then
            isPDF = True
            Exit For
        End If
    Next
End Function



There are probably a couple of other things that could be said, but I'll leave those to another reviewer.