I have made it work with Reformation reform and so far it seems like there are no conflicts or bugs associated with the merger and it should work with 4 doctrines and 6 doctrines versions, though I doubt 4 doctrines version is needed as Reformation Reform has 4 doctrines included in it(if I am not mistaken). this is how I merged these two mods.

1. download both mods and unzip them.

2. Go into Reformation Reform folder>Common>Religion Features > 00_features.txt> search Religion_doctrine by pressing Ctrl+F and have the line below "religion_doctrine = {" look like this -" buttons = { doctrine1 doctrine2 doctrine3 doctrine4 doctrine5 doctrine6 doctrine7 doctrine8 doctrine9 } " and save the file.

3.Go to 9 doctrines file>GFX>Interface>Reformation and copy Reformation_view_bg.dds, then go to reformation reform folder>GFX>Interface>Reformation and paste and overwrite Reformation_view_bg.dds.

4.Go to 9 doctrines file>Interface and open Religion_reformation.gui(this is the main folder that causes these two mods to conflict with each other, so it is crucial that you do it properly) as a notepad or notepad+. search for name = "nature" by Pressing CTRL+F. upon locating this wall of text -

windowType = {
name = "nature"
position = { x=90 y=190 }
moveable = 0
fullScreen = no
Orientation = "UPPER_LEFT"

instantTextBoxType = {
name = "label"
position = { x = 15 y = -40 }
font = "vic_36_black"
text = "REFORMATION_NATURE"
maxWidth = 170
maxHeight = 20
fixedsize = yes
format = centre
}

guiButtonType = {
name = "picture"
position = { x=0 y=15}
quadTextureSprite ="GFX_religion_feature_uncertain"
clicksound = bookmark_click
pdx_tooltip = "REFORMATION_SELECT_FEATURE"
}
instantTextBoxType = {
name = "feature_label"
position = { x = 10 y = 150 }
font = "vic_22_black"
text = "feature_uncertain"
maxWidth = 173
maxHeight = 20
fixedsize = yes
format = centre
}
}
delete it. after you delete it your screen should look like this (without any extra spaces, I am newbie when it comes to the modding so I don't know the consequnces of mismanaged spaces p.p) -

instantTextBoxType = {
name = "reformation_label"
position = { x = 400 y = 57 }
font = "vic_36"
text = "REFORMATION_REFORMATION"
maxWidth = 250
maxHeight = 20
fixedsize = yes
format = centre
}

windowType = {
name = "doctrine1"
position = { x=389 y=190 }
moveable = 0
fullScreen = no
Orientation = "UPPER_LEFT"

after you have done all this you can save the file. after saving the file copy the modified religion_reformation.gui, go to Reformation reform folder > Interface and paste and overwrite religion_reformation.gui. now let's explain why these two mods conflicted with each other - the explanation is fairly simple, reformation reform basically erases the whole "Nature" aspect of reformation and every doctrine influences the nature of the religion, as such incorporating the window into the game that should be important but is overwritten in such a way that it doesn't exist anymore, causes the game to derp out and crash. Hope this helps, but I am in no way confident it will work 100% of the time, though as far as testing this goes - religion window works perfectly fine, though I haven't had time to reform the religion using these two merged religions.