Shares of electronic-document specialist DocuSign (NASDAQ:DOCU) have been on a tear recently. The stock is up more than 200% over the past 12 months and over 100% during the last three months alone.

Investors are bullish on DocuSign because of the company's excellent execution recently and its strong positioning as a beneficiary from growing work-from-home trends. When it reported results for its first quarter of fiscal 2021 earlier this month, the company demonstrated more strong revenue growth, fueled by organizations' accelerating digital transformations.

Here's a look at the impressive business growth propelling this growth stock higher.

DocuSign's e-signature product on a laptop and smartphone

Image source: DocuSign.

1. Accelerating revenue growth

Investors have watched DocuSign's top-line growth closely since the company's initial public offering two years ago -- and the figure hasn't disappointed. In fact, DocuSign's year-over-year revenue growth rate accelerated in the first quarter of fiscal 2021, rising 39% year over year -- up from 38% growth in the fourth quarter of fiscal 2020. 

"Led by eSignature, our Agreement Cloud offerings are not only helping customers carry on with business in this time of crisis, but will continue to deliver value as the world emerges from it," said DocuSign CEO Dan Springer in the company's fiscal first-quarter earnings release earlier this month.

2. Rapid growth in large customers

Particularly notable in fiscal Q1 was the company's significant acceleration in the growth of its enterprise and commercial customers -- a customer base that is primarily made up as companies in the Global 2000, as well as small and medium-sized businesses with 10 or more employees.

This customer group increased 49% year over year during the period, outpacing total customer growth of 30%. In the fourth quarter of fiscal 2020, enterprise and commercial customers grew 33% year over year, and total customers increased 24%.

3. Strong operating cash flow

Thanks to its ability to throw off meaningful positive cash flow, DocuSign is able to invest aggressively in the growth opportunities in front of it. Fiscal first-quarter operating cash flow was $59 million, up from $46 million in the year-ago period.

Free cash flow, or operating cash flow less capital expenditures, was also notably positive. Free cash flow in fiscal Q1 was $33 million, up from $30 million in the same quarter last year.

4. An improving non-GAAP operating margin

While DocuSign isn't profitable yet on a generally accepted accounting principles (GAAP) basis, the company is demonstrating strong operating leverage. This suggests DocuSign's profitability on a per-dollar of revenue basis will likely improve as revenue grows.

DocuSign's non-GAAP operating profit was $23 million, or 8% of revenue. This compares to a non-GAAP operating profit of $10 million, or 5% of revenue in the year-ago quarter.

5. Robust guidance

Following a strong fiscal first quarter, management lifted its full-year revenue outlook. DocuSign now expects fiscal 2021 revenue to be between $1.313 billion and $1.317 billion. This is well ahead of the company's previous forecast for revenue during the fiscal year to be between $1.272 billion and $1.276 billion.

With impressive underlying business execution recently, it's not surprising that investors have been bidding the e-signature company's stock higher.