ok, i start here with feedback. I will edit this post until you answer, then start the next one.
I start on page 2; and then goes on through all pages: It would be nice to have two columns of text for readability. Maybe you ask Mitchiemacha for some comments on text layout as he is good in those things.
Page 4,
preface:
A new line after "Greetings and welcome to HeroQuest!"
There's enough space on the page. I am a fan of little drawings in the empty spaces but that is of course up to you - i am fan of drawings but can't draw, for example

Page 6,
character creation & sheets - would be nice to have an image of the character sheet in here.
By the way I had to crank up the zoom to 150% to read it - chemotherapy does strange things to the eyes and that was a little bit to small. It would not have been too small a week ago; crazy as it sounds.
Character classes: I like the special rules you invented there, on first glance nothing seems too strong or too weak. However, i did not see the rest of the rules yet so I better don't judge yet. I couldn't resist to go cleptocreative on the Inventor special rule.
The stealth special rule seems to be made for single player games? It is a step to go for my long-dreamed-of dark-and-light-and-sneak-around scenario i dream of since 2012 but couldn't quite get a grip on so far. Rule stolen.
Schools of Magic: You state
Monsters and Heroes may always have at least 1 movement die, 1 attack die and 1 defence die
That's a general rule, but it is stowed away under schools of magic. Might there be a better place for this sentence? Is there a contradiction with the monster movement rules (no dice)? Oh well, i did not yet see your monsters, though.
Spells:
I like to separate cards in cost, range, target, effect and flavor text.
You set up some general rules for range and target but you said nothing on cost. Do I assume right that the spellcaster must discard the card as cost? If yes, it might be worth a sentence under the headline "Schools of Magic"
Pass Through Rock wrote:Allows movement through walls, if you move in to a new move you must stop and allow the DM to place the room’s contents on to the board. You may not travel through furniture nor monsters unless you have Veil of Mist cast on you.
If you end your movement inside a wall then you die instantly and lose all items and gold.
First, it's nice to have the double action directly mentioned on the card. Second, i marked a word in red that should be different possibly?
Cavern Darkness wrote:Choose 3x3 squares. No missile or spell can be fired/cast in/out/through those squares. Anybody in those squares may only move 1 square per turn and may not Dash. The effect lasts for the rest of the quest. Room only.
I like to have all range specifiers in one place, so i would maybe rephrase it_
Choose 3x3 squares inside a room. No missile or spell can be fired/cast in/out/through those squares. Anybody in those squares may only move 1 square per turn and may not Dash. The effect lasts for the rest of the quest.
There is no mentioning of close combat - is it easy to cc in complete darkness? ? By the way, that's a spell that might well fit into detection, if you widen the concept to anything connected to detection; also the protection from detection. And yes, it has been stolen.

Flesh to Stone wrote:Monster must roll equal to or less than maximum Body Point score on 2D6. If they fail then they are turned to stone and may not move, perform any action or defend themselves. At the end of their turn the monster may repeat the roll to try to break free if they fail then they lost 1 Body Point without being able to defend.
You specifically mention a monster as a target. Is that intentionally? If it can be used on Heroes, Men-At-Arms and others, too, I would reword it like so; i also added some interpunction:
Flesh to Stone wrote:The target figure must roll equal to or less than their maximum Body Point score on 2D6. If they fail then they are turned to stone and may not move, perform any action or defend themselves. At the end of their turn the monster may repeat the roll to try to break free. If they fail then they lose 1 Body Point without being able to defend.
There is a second remark: It is pretty much an autokill-spell or maybe I misunderstood a detail. It is difficult with 2d6 to roll 4 or less, and many bosses have just those 4 or 5 BP; also our own beloved wizard.
Does the target lose 1BP each round until it dies or de-stones or does it just lose 1 BP?
I propose one of those alternatives in comparison. (sorry I don't know the forum's table format very well - just import to excel, it's comma separated)
rolling same or below the BP with
1BP,

,
2BP, 3%,
3BP, 8.4%,
4BP, 16.7%,
5BP, 27.8%,
6BP, 41.7%,
rolling same or below the BP with
1BP, 16.7%,
2BP, 33%,
3BP, 50%,
4BP, 67.7%,
5BP, 83.3%,
6BP, 100%,
rolling 1 white die per starting BP, looking for
1BP, 16.7%,
2BP, ~31%,
3BP, ~42%,
4BP, ~52%,
5BP, 60%,
6BP, 66.6%,
rolling 1 white die per starting BP, looking for

:
1BP,

,
2BP, 11.1%,
3BP, 25.9%,
4BP, 40.7%,
5BP, 53.9%,
6BP, 64.8%,
That's it for today. Tomorrow's another day.
Yesterday they gave me something that made it difficult to keep the eyes straight so I just streamed Dr. Who.
Today I wasted much of the chemo time on Warhammer Quest.
Let's see tomorrow.