The translation in your OP is wrong in many sections and it may even changed the entire context entirely. Its quite misleading, so you should really change it. I'll provide a translation thats more accurate.
OP Raw text:
几百年后,函谷关。 白发的老人面前,关隘的守将正崇敬地看着他: “您真的见到了,传说中的“道”吗?” “没错。”
老人温和的声音,宛如普泽的细雨,平复了守将心中 的焦急。
“道就在那里,它在门后,也在门内。门”并不存 在,但可以被看到,这正是其玄妙的根源......"
一个个梦幻的泡泡在函谷关上升腾了起来,老人的身 影随着泡泡一起慢慢升临到半空中,身后那片琉璃的 世界令守将目眩神迷。而他的声音还在不断响起: “道,可道,非恒道也。由泡所发,向泡而生。 名,可名,非恒名也。出泡而形,入泡而真。 门,始终万物,玄妙之根,泡断影灭,生死相成...... "
就在老人彻底消失之后,守将整理了他留下来的言语 ,并著成一书。但他删去了关于“泡”的描述。 不过,仍有人捕捉到了关于“泡”的蛛丝马迹,为了 找到“泡”,人们将与其形貌相似的丹道视为通往“ 泡”的路径。
据说,当炼丹士们服下真正的金丹以后,他们就能抵 达玄妙之门,得到“泡”赐予的无上智慧。
Enhanced translation:
Hundreds of years later, Hangu Pass (most likely referring to the real life location in China). In front of the white hair elderly man, stood a general of the pass who looked upon him with deep reverence, said "mister, have you really seen the legendary "tao" before?" The old man replied: "Indeed"
The voice of that old man was as soft as the rain of Puze (reference to Pouzay, a commune in France), subsided the anxiety in the general's heart.
"The Dao is there, it is behind the door, and it is within the door. The door actually doesn't exist, but it can be seen, it is the root of the Dao's mystery......."
Dream bubbles ascended to the Hangu Pass one by one, the elder's shadow gradually ascends along the dream bubbles into midair, the color-glazed world behind him made the general dazzle. And his voice continuously ringed out, "
The Tao that can be spoken is not the Eternal Dao. It rises from bubbles, it grows from bubbles. The name that can be named is not the Eternal Name. Out of the bubble it forms, into the bubble it becomes real. Door, always everything, the mysterious root, cut from the bubble and comes annihilation, intertwining life and death......"
Right after the elder man completely vanished, the general organised his words left behind, and wrote a book about it. However, he deleted the descriptions about the "bubble". However, there are still those who grasps clue about the "bubble", and to find the "bubble", they'll deem other Dan Dao (
see here for definition of 丹道) with a similar appearance to it as a path that will lead to ”bubble".
It is said that when alchemists grasps hold of the real golden Dan, they can
arrive at the mysterious gate, acquire the boundless knowledge bestowed by the "bubble".
Your translation:
Hundreds of years ago, at the Hangu Pass.
Before the white-haired old man, stood a defender of the pass that looked at him with reverence.
"Have you truly seen the legendary "Tao"?"
"That's right."
The gentle voice of the old man, like the fine rain of Puze, calmed the anxiety in the guard's heart.
"The Dao is right there, it's behind the door, but also inside the door. The door itself doesn't actually exist, but it can still be seen. This really is the origin of all which is mysterious."
A dreamy bubble rose up from the Hangu Pass, and the old man's figure slowly rose up into the air along with the Bubble, the crystalized world behind him dazzling the guard. And his voice continued to ring out:
"The Dao that may be trodden is not the eternal Dao. It arises from the bubbles, and towards their direction it is born.
The name that can be named is not the eternal name. Coming forth from the bubbles it takes form, yet entering them it becomes real.
The door is the beginning and end of all living beings, it is the root of that which is mysterious. As bubbles are cut short and shadows are extinguished, life and death complement each other."
Just after the old man completely vanished, the guard compiled his words into a book. However, he removed the descriptions of these "bubbles".
Yet, there still are people who were able to grasp the still threads reminiscent of the Bubble. In order to capture the Bubble, people will look through the path of the Bubble together with the Golden Dan which resembles it.
It is said that after the scholars who practice alchemy have consumed the true Golden Dan they are able to penetrate through the door and acquire the Bubble's blessings and knowledge.
I'll explain whats wrong with your translation later. Busy right now.
