The CKFinder is component of CKEditor (WYSIWYG editor used by In-Portal) for uploading files (documents included) that can be later downloaded from website. It has a restriction on document types that can be uploaded.
The old style document formats (e.g. "doc", "xls", etc.) are allowed, but new style document formats (e.g. "docx", "xlsx", etc.) are not.
Allow MS Office 2007+ document formats to be uploaded in CKEditor.