IncludeText field

Hi I am absolutely confused with Includetext field when it comes to hyperlinks.

We use an internal document management system and I need to link 1 document to 1 main document. Both documents are within the system.

Prior to our internal DMS system we had a simply structure and I simply used the following command to link contents of 1 document to the other one - see below:

{INCLUDETEXT "I:\\shared\\client standard documents\\fad\\Fd5_15a.doc" \! \* MERGEFORMAT }

Now we use a intranet DMS system and the reference of the document to be linked is stored as:

http://plexus.calfordseaden.co.uk/DMS/view_document.asp?ID=1157648

I have tried to add the INCLUDETEXT field as follows:
{INCLUDETEXT "http://plexus.calfordseaden.co.uk/DMS/view_document.asp?ID=1157648 \* MERGEFORMAT}

However I keep getting invalid filename. Please help as I am absolutely desperate to resolve this.

Many thanks in anticipation.