MSA的文档上有说职业证明的问题：
Documentary evidence in support of work experience claims
must be on a company letterhead (including name and
location details) and include the date of document, name and
status of author, dates and duration of employment and the
title of position occupied.
比如之前公司的老板作为我的推荐人，写了个职业证明
但是没有前公司的公章，这样可以么？
另外此证明也是需要公证的是嘛？