Add spaces around variable with $ symbol bookends
Here's a version using Regular Expressions. 

Option Explicit

Sub SpaceVarsAndEqns()

    Dim DocumentRange As Range, ParagraphRange As Range
    Dim i As Long, P As Paragraph
    Dim Pattern As String, Replace As String, RegEx As New RegExp
    Dim ParagraphText As String

    Pattern = "(?:\s?)\$[^$(]*\$(?:\s?)"
    Replace = " $&amp; "

    With RegEx
        .Global = True
        .MultiLine = True
        .IgnoreCase = True
        .Pattern = Pattern
    End With

    Set DocumentRange = ActiveDocument.Range
    For i = 1 To DocumentRange.Paragraphs.Count
        Set P = DocumentRange.Paragraphs(i)
        ParagraphText = P.Range.Text
        If RegEx.Test(ParagraphText) Then
            P.Range.Text = RegEx.Replace(ParagraphText, Replace)
        End If

    Next

End Sub


Before:

\begin{bmatrix} $eval(($d$*$d.pmv$)/(|$d.et$|)*($d.et$*$xm$) + (($b$*-1)*$d.pmv$)/(|$d.et$|)*($d.et$*$ym$) + $dist5$,0.###)\\ $eval((((($a$*$d$)-$d.et$)/($b$))*$d.pmv$*-1)/(|$d.et$|)*($d.et$*$xm$) + ($a$*$d.pmv$)/(|$d.et$|)*($d.et$*$ym$)+ $dist6$,0.###) \end{bmatrix}

After:

\begin{bmatrix} $eval(( $d$ * $d.pmv$ )/(| $d.et$ |)*( $d.et$ * $xm$ ) + (( $b$ *-1)* $d.pmv$ )/(| $d.et$ |)*( $d.et$ * $ym$ ) +  $dist5$ ,0.###)\\ $eval((((( $a$ * $d$ )- $d.et$ )/( $b$ ))* $d.pmv$ *-1)/(| $d.et$ |)*( $d.et$ * $xm$ ) + ( $a$ * $d.pmv$ )/(| $d.et$ |)*( $d.et$ * $ym$ )+  $dist6$ ,0.###) \end{bmatrix}



This requires adding a reference to the Microsoft VBScript Regular Expressions 5.5 by going to Tools > References and checking that box:



You can read more on Regular Expressions in VBA in this Stack Overflow answer.