Cannot download Yosemite 10.10.0, where can I find the dmg File?

Where are you seeing that you need Yosemite first, this should not be the case.

Apple has removed the full installer for Yosemite, you can upgrade directly to El Capitan if your Mac is too old to upgrade to Sierra or High Sierra. How to download OS X El Capitan - Apple Support

When Apple launches a new OS they start at for example Yosemite 10.10.0, but when Apple introduces an update they replace the initial full installer with the next so it will now download as 10.10.1, and this will continue to happen till Apple releases its final update for that particular OS, in Yosemite's case that was 10.10.5.

If you go ahead and download El Capitan the version you download will be 10.11.6.

As I said if your Mac is too old for Sierra and High Sierra you can download and install El Capitan. Now that we know you have a 2013 iMac, then you can upgrade to High Sierra, the App Store notices that and refuses your request to download El Capitan. So you can download High Sierra direct from the App Store Featured section, or you could download Sierra which is still available, How to download macOS Sierra - Apple Support

If you still want El Capitan you can download that on an older Mac that cannot upgrade to Sierra or High Sierra and then transfer the Install Mac OS X El Capitan.app (Applications folder) to your iMac. Note you will need to use your AppleID to sign in to the App Store on the other Mac to download it.

If you are going to upgrade make sure any third party apps you use have updates available so they can be used in the new OS, and also check with the manufacturers of any printers/ scanners or other hardware you use have driver and software updates available so they will continue to function in the new OS.

Dear Eau Rouge, it seems to be strange, but I also need to downgrade from High Sierra to Yosemite 10.10.x. (after upgrade from Snow Leopard!) The x is for something between 0 and 3, not much higher. The reason: my graphic card is used for scientific calculations by an app. Therefore it needs the CUDA driver. But the latest driver, accepted by OS, do not support my GPU. After extensive mail traffic with Nvidia they find the only solution: downgrade to OS X 10.10.x so I can install the 6.5.45 CUDA driver wich support my GPU.(hopefull) It's not always useful to update, upgrade....

It has to do with the original question ! I'm sorry, but the original question is 'Cannot download Yosemite 10.10.0, where can I find the dmg File?, right? Maybe I don't had to describe my problem in detail, like I did.

This was the same question I had, 'where can I get Yosemite .dmg' download ! Inbetween the problem I had disapeard by itself. Maybe not for ever, but it's gone.

If you had downloaded Yosemite at the time it was available to download then it will appear in your Purchased section of the App Store and you should be able to download it again. If not then the best bet is to make a Genius appointment at an Apple Retail Store and ask them to put it on a USB stick that you supply, the version they will give you is 10.10.5. You will need to erase your Mac and install the OS that came with it then upgrade to Snow Leopard and update that to 10.6.8 before you can install Yosemite. There is no .dmg for the full installer, only the incremental and Combo updates are available as .dmgs, but you won't need those as the App Store and the Retail Store will give you the 10.10.5 full install.

If you really need an earlier version of Yosemite such as 10.10.3 as you say above you will need to contact the Apple Retail Store to see if they can accommodate you.

Enzeddev wrote:

I have 10.9.5 and downloaded high sierra and it still says i have 10.9.5 installed? ***? And yes i downloaded from the app store!

If the installer wasn't launched after the download completed, did you click on the Install High Sierra app in Applications, and run through the High Sierra software installation? If the installer somehow didn't open automatically after the download was completed, or if the installer was closed after the download without being run, there won't be an upgrade performed.

Application Compatibility

Do a backup before installing, preferable 2 backups on 2 different drives.

What is your point, this has nothing to do with the original question from the OP over a month ago.

If you have a question to ask or need advice post your own query.

I have 10.9.5 and downloaded high sierra and it still says i have 10.9.5 installed? ***? And yes i downloaded from the app store!