Whatever else happened to it, the likelihood that it became encrypted when
you used spell check is close to zero. Perhaps you could explain in a little
more detail what you did and what the result actually is, and maybe someone
will be able to help.
If your document is damaged in some way, which is possible, then it may be
possible to retrieve some of it - it rather depends on what you are seeing
and what you are able to try - and also what version of Word, or, at least,
what version of the Word document format, you are using. Alternatively, as
you are doing a monthly report, I presume you are in a corporate
environment, and should have backups.
