What's the form for the HR letter I need to include with the Schengen visa application?

The purpose of the trip is not required, unless your office is paying for your trip; and this is a different letter than the standard salary certificate.

The salary certificate should state:

1. Your full name, as stated in your passport.
2. Your position
3. Your passport number (if you are a permanent resident, otherwise your national ID number if you are a citizen)
4. The date you are first employed
5. Your total salary

It must be signed by an authorized party from your HR office, even if it is computer generated.

Now, in your particular situation what you need to supply is an invitation letter from your host company stating the nature and purpose of your visit. It should include the following details:

1. Your full name, as stated in your passport and your passport details.
2. The purpose of your visit.
3. The dates of your visit.
4. The information about the host, their address, their contact number and their tax identification code (or other government identification number, such as a business license number).
5. If the host is paying for, or otherwise assisting with the trip.
6. The letter must be on a letterhead, and it is best if it is signed.

Here is a sample:

The signature is not always required - for my friend applying for the first time to Hungary they asked for as signature; for myself applying to the Netherlands they didn't care if the signature was there or not (and we were both being invited by the same organization).

You need to attach this letter, a picture with a white background, a filled in standard Schengen application (pay particular attention to the part about paying for the expenses of the trip, and check the right boxes), a certified current bank statement (at least three months is required), itinerary, travel details and accommodation details.

At least in Middle East, Schengen embassies want HR to say in a letter that We know Mr. XYZ wishes to go to Country ABC for tourism purpose from 11/22/33 to 44/55/66, and we have no objection to it. Mr.XYZ's proposed date of resuming duty is 77/88/99.

More specifically, embassies require the following included in a No Objection Certificate (NOC) from the employer:

1. Name, passport number, resident number
2. Position in company, all salary details, date of joining
3. Leave dates, paid/unpaid, date of expected return
4. No objection for touring the requested country
5. Company computer card (sponsor signature samples, company stamp sample)

At the same time, in most of the Middle East, you need permission/NOC from your employer/sponsor for almost anything (buying a car, getting a licence, renting a house, going out of country, changing jobs etc.), so the above might be specific to the region.

You might ask whether the HR letter can cover just the basic details, and not mention the purpose of the trip. If you would indicate your country, responses could shed more light.