VBA Code

With Selection.Cells 
   .Borders(wdBorderType.wdBorderLeft).LineStyle = wdLineStyle.wdLineStyleNone 

   With .Borders(wdBorderType.wdBorderRight) 
      .LineStyle = wdLineStyle.wdLineStyleSingle 
      .LineWidth = wdLineWidth.wdLineWidth075pt 
      .ColorIndex = wdColorIndex.wdAuto 
   End With 

   With .Borders(wdBorderType.wdBorderTop) 
      .LineStyle = wdLineStyle.wdLineStyleSingle 
      .LineWidth = wdLineWidth.wdLineWidth075pt 
      .ColorIndex = wdColorIndex.wdAuto 
   End With 

   With .Borders(wdBorderType.wdBorderBottom) 
      .LineStyle = wdLineStyle.wdLineStyleSingle 
      .LineWidth = wdLineWidth.wdLineWidth075pt 
      .ColorIndex = wdColorIndex.wdAuto 
   End With 

   .Borders.Shadow = False 
End With 

Different objects have different borders
A border can be defined by using three properties.
You must always set the LineStyle first
LineStyle -
LineWidth -
Color -

objCharacters 
objParagraphFormat 
objRange 
objSection 
objSelection 
objTable 
objTableStyle 
objFont.Borders(wdBorderType) 
objFrame 
objParagraph.Borders(wdBorderType) 
objRow 
objColumn 
objCell.Borders(wdBorderType) 
objStyle.Borders(wdBorderType) 

Not every linestyle is available in every width
If you choose a linewidth which is not compatible with the line style you will get an error.

Borders.Visible

You can set the visible property of a border.
This is the equivalent to setting the linestyle to wdLineStyleNone

objSelection.Borders(wdBorderTop).Visible = False 
objSelection.Borders(wdBorderTop).LineStyle = wdLineStyleNone 

If you set the visible property to True a black wdLineStyleSingle border is applied
The LineWidth is a bit hit and miss

Removing all Borders

The quickest way is to use the Enabled property

objSelection.Borders.Enable = False 

This removes all the borders
This property however will not remove diagonal borders from a table or table style object.

Enabled Property

This returns wdConstants.wdUndefined if border formatting is applied to all or part of the object.
This applies to all borders of the specified object
True - sets the linestyle to the default line style and the line width to the default line width.

Default Line Style and Width

These can be set using

Options.DefaultBorderLineWidth = 
Options.DefaultBorderLineStyle = 

Outside Borders

These are the top, right, bottom and left borders of an object
OutsideLineStyle
OutsideLineWidth
OutsideColor

Inside Borders

InsideLineStyle
InsideLineWidth
InsideColor

If the line style = wdlinestylenone
then what is the color and linewidth