pkiexample.js

const WebCrypto = require("node-webcrypto-ossl");
const crypto = new WebCrypto();
const fs = require('fs');
const asn1js = require('asn1js');
const pkijs = require('pkijs');
const pvutils = require('pvutils');

function parsePKCS12Internal(buffer, password)
{
	//region Initial variables
	let sequence = Promise.resolve();

	
	const passwordConverted = pvutils.stringToArrayBuffer(password);
	//endregion
	
	//region Parse internal PKCS#12 values
	const asn1 = asn1js.fromBER(buffer);
	const pkcs12 = new pkijs.PFX({ schema: asn1.result });
	//endregion
	
	//region Parse "AuthenticatedSafe" value of PKCS#12 data
	sequence = sequence.then(
		() => pkcs12.parseInternalValues({
			password: passwordConverted,
			checkIntegrity: false
		})
	);
	//endregion
	
	//region Parse "SafeContents" values
	sequence = sequence.then(
		() => pkcs12.parsedValue.authenticatedSafe.parseInternalValues({
			safeContents: [
				{
					// Empty parameters since for first "SafeContent" OpenSSL uses "no privacy" protection mode
				},
				{
					password: passwordConverted
				}
			]
		})
	);
	//endregion
	
	//region Parse "PKCS8ShroudedKeyBag" value
	sequence = sequence.then(
		() => pkcs12.parsedValue.authenticatedSafe.parsedValue.safeContents[0].value.safeBags[0].bagValue.parseInternalValues({
			password: passwordConverted
		})
	);
	//endregion
	
	//region Store parsed value to Web page
	sequence = sequence.then(
		() => pkcs12
	);
	//endregion
	
	return sequence;
}
var file = new Uint8Array(fs.readFileSync("firmaultima.p12")).buffer;
console.log(parsePKCS12Internal(file, 2002));

@variux You forgot "setEngine" call:

const WebCrypto = require("node-webcrypto-ossl");
const webcrypto = new WebCrypto();
setEngine("newEngine", webcrypto, new CryptoEngine({ name: "", crypto: webcrypto, subtle: webcrypto.subtle }));