You can order a copy of the pension application from the Military Records Research Service http://history-sites.com/research/index.html
Widow's pension applications vary greatly in details. The best will include details of the late husband's service; date of marriage; some genealogical information (date and place of birth, death, etc.); length of residency in the State of application; financial information (Confederate pensions had a means test -- limits on income, value of real property, etc.); affidavits of the husband's wartime comrades, etc.
Of course, some contain only minimal information. But there should be enough to verify the veteran's service.