Your use of the term "pension" to mean a 401(k) account is very confusing, which I suspect is why you have not gotten many responses.
In general, you may transfer ("rollover") pre-tax money from a 401(k) from a former employer to a traditional IRA. For a former employer, you may do this at will. If we are talking about your
current employer, the rules of that plan may or may not allow it.
Here is a chart from the IRS that shows the allowed rollover pairs:
https://www.irs.gov/pub/irs-tege/rollover_chart.pdf