The branch of forensic science called questioned document examination is responsible for providing evidence about documents that seem suspicious or questionable. Document examiners may question a document based on "alterations, the chain of possession, damage to the document, forgery, origin, authenticity, or any other questions" ("Questioned Document Examination," Wiki). Document examiners may inspect a document based on handwriting by comparing a document to another sample of handwriting. An examiner may perform a handwriting analysis by noting important characteristics of the handwriting in question and then comparing it to a known sample. After comparing the handwriting on the document in question to the known sample, the examiner will then note similarities and differences between the two to decide which similarities and differences are and are not important. Any person's handwriting will vary day-to-day or over an extended period of time; however, both the uniqueness and frequency of differences help show whether or not the handwriting has been forged. The examiner may also need to have a peer review the handwriting to confirm that the handwriting has indeed been forged.
Other than handwriting analysis, an examiner may identify ink used, conduct ink comparisons, examine a seal, rubber stamp impressions, examine typewriter ribbons, and typed text. An examiner may also analyze paper used, and match paper cuts, tears, or perforations found on a piece of the document in question with another document to see if the two at one point made a whole document, which can help prove alterations and forgeries.