Overstriking with an “attached” comment may be achieved using the
pdfcomment package, to which you can give optional arguments
with all sorts of detail. The comment text is encoded using an Adobe
“annotation”; unfortunately, support for these annotations is not a
common feature of PDF viewers, but if you can safely assume
that your audience will use
Acrobat Reader, the facility
provides that extra “shine” that business users so love.
Overstriking for cancellation in maths expressions is achieved by a different mechanism.
Documentation of ulem is in the package file.
Source: Overstriking characters