The following Macro will find blank lines in a Word document and remove them:
Private Sub DeleteBlanks()
.Text = "^p^p"
.Replacement.Text = "^p"
.Execute Replace:=wdReplaceAll, Forward:=True, _
This Macro finds single blank lines, and it would have to be re-run to remove double blank lines. If multiple blank lines is an issue, the macro could be extended to remove say all groups of 3 blank lines, then all pairs of two, and finally any remaining single blank lines.
Please note that the changes made by this Macro may not be reversible using the Undo function, so always make a backup before running a macro.
Alternatively you can do the same using Word's Find and Replace dialog box.
In the Find box enter ^p^p
and in the Replace box enter ^p