Can I transfer Flash cs5.5 to another computer?

Yes, that is possible. You shall have to install a copy of Adobe flash and you need to have a valid serial key to do that.

But only attempts of activation are possible.

No, you may not transfer programs, you need to do a fresh install

Put your disc in the drive and enter your serial number when asked

If you do not have an install disc, and you did not save your install download, you are probably out of luck

NOTE - CS3 and earlier are COMPLETELY gone from the Adobe file server
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The process below USED to work (until April 14) if you bought a download direct from Adobe... an employee is trying to find out why this process no longer works, so IF you bought a download direct from Adobe, check back every day to see if the process starts working again
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For CS6 back to CS4 you may download ONLY if you bought direct from Adobe via download
-Log-in to your account and click this link https://account.adobe.com/products
--click Order history on the left and then the link to your order that will show on the right
--and finally click the link "Downloads and serial numbers" that will appear
--as always, write the serial number in a text file AND copy that text file and the
---download file(s) to an external drive (or two) to be sure you have what you need
-if you did not buy direct from Adobe via download you must find your original install
--if you have an Education or volume license you MUST use your original media
--the link for an Education or volume license download is not available at all
-if you bought a disc and don't have a drive you will need to buy an external USB drive
-if you bought a download from a 3rd party vendor you will need to contact that vendor

If you have the original installation media and a valid serial number, it should be possible. Activation servers for CS4 through CS6 are still online. You may have to contact customer support for a reset of the number of activations (only 2 activations allowed).

However, Flash support ends this year. No browser will allow Flash files to play after December 31, 2020.