It depends on what you mean by "copying" Microsoft.
As Microsoft is such a famous company, and one of the few well known companies who's name ends with "-soft", then it could be argued that you are copying Microsoft.
A better question however, would be "is it legal to use -soft". While I am not a lawyer, I believe it is perfectly acceptable to do so.
Trademark laws exist to stop one business gaining an unfair advantage by leeching off the name or image of another company. To prevent this, companies can register and trademark their names and logos.
I do not think it is possible to register just the extension "soft", as it is too widely used to be considered unique. Only if your name sounded like "Microsoft", would you be in violation of their trademark - i.e "Mike Row Soft".
So while you may be seen as copying Microsoft by naming your company that way, you are more than entitled to do so legally.
(However seek formal legal advice from a real lawyer before proceeding)
To me, soft is associated with software more than Microsoft, but to each his own. Unless you're using the name "Microsoft" inside your name, there should not be an issue. (Example: Microsoft Services is illegal)
Ask a few of your future prospects about the name and what they feel about it, and base your choice upon their responses. They're the people to whom the name will be most meaningful.
I wouldn't think in this day and age that it's directly copying Microsoft, I can't speak for most people but since a lot of people don't know Microsoft is an abbreviation for
Microcomputer Software, then they won't realize it. I wouldn't think of Microsoft when I hear Perrysoft, and there are video game development companies with the 'soft suffix also.
If, on the other hand, you decided to name your company iSoft , then you might catch heat from the other side....