OED:
herewith:
1. Old English–
With this; along with or together with this.
2. a1400–1546
† At the same time with this; upon this; with these words, etc. Obsolete.
3. 1560–
By means of this; hereby.
herewith:
1. Old English–
With this; along with or together with this.
2. a1400–1546
† At the same time with this; upon this; with these words, etc. Obsolete.
3. 1560–
By means of this; hereby.