I downloaded 1.4 on steam and I had more than 300M. But stupid I decided to trash a AAA game then start a console while doing some research then develop an engine and train staff until engine is finished. And I didnt check money status. Now i have 394K. 
Until this version you could edit save file with GDT SaveEditor or SQLite DB Editor by finding “cash” in slot.
Now save folder is changed. I found it. GDT Editor gives error. What i edit through sqlite doen’t effect anything.
Zomg you might have to resort to strategy!
Or, follow this text tutorial. first go to C:/Users/Local/Packages/b3b9bb81_swksbykws6pr
Then select “RoamingState” and select file folder and open it with notepad.
find “Cash” and edit it.
(note: also edit “auto”) I also know of a video tutorial. Heres a link:
Its is outdated way before what I said. Now they dont use that save system.
all methods are outdated yet.
the files are now a sqlite format which can only be edited with an sqlite browser.
but be warned and make backups! you can corrupt your files very fast in that way without knowledge…
I edited with sqlite before. I was succesful. Now my editations change nothing.
Game Dev Tycoon uses Stean Cloud. Your progress will get saved on servers of Steam Cloud, which will be used. And you can’t change stuff on the servers off Steam. 
Actually with the steam version, it became quite easier.
Locate your steam folder.
Steam\userdata[yourID]\239820\remote
open up slotauto or your specific save slot with any good editor, i.e notepad++ or ultraedit etc… Modify away. Exact same as the old sqllite trick except they are extracted out individually now. Make sure you open up steam right click on the game and disable cloud synchronization. GG 
When you modify the cash amount, even though when you click load the amount shown will not represent the amount actually found in the game. Any problems I’ll be around
Thx. I added 25M and I survived!
Just after 1 year I earned 1000M cuz I released console new engine SDK and a AAA MMO game!