A family of Microsoft word processing software products for creating web, email, and print documents.
An example would help, as John has already suggested. You can start with a screen shot and possibly also share a sample of the resulting Word document (remove any sensitive information).
Generally, any table that you paste in from an external source may have fixed dimensions so that it does not fit in between the margins in a Word document. Fixing it may require that you change the width of the table as a whole and also the width of individual table columns. Which specific options have you tried so far? A good starting point is Table Layout tab > AutoFit > AutoFit Window. This will adjust the table width to 100%.
Sometimes, the quickest fix is to convert the table to text and then convert it back to a table.