Open REL File
A RELS format file is a metadata file contained inside Microsoft Open Office Open Office XML documents.
RELS type of files stores XML specifications for how the "parts" of a "package" are connected to form a document.
RELS files are stored in a _rels directory of an Open Office XML document.
RELS files are not intended to be opened manually, however, being an XML file, it contains editable text. You should not edit the content as it may render the document that contains the RELS file unusable. Instead, use the file is referenced by the Microsoft Office application that opens the document that contains the RELS file.
Software to open RELS files
As noticed before, the RELS files should not be opened or edited, however, you can open it, after changing the Open Office document extension to ZIP, and then looking for the _rels folder. In this folder you will find the RELS file, which you can open with the following software package: