Hi i wanted to save as pdf so I do save as and choose pdf but then I don't understand the restrict to pdf version 1.5 or 1.4.What does it mean?
I want people to be able to open the files with any version of acrobat reader.Am i restricted here by the version of acrobat reader?
I want to put the pdf files in my site so they can be downloaded so it's important to me that no matter what adobe reader people have they would be able to open it.

Some new specifications are regurarly added to the pdf format so to be able to use those new features the users are required to update to a new version of acrobat designed to handle them.
To be able to read pdf version 1.4 (published in 2001) you need Acrobat >= 5.0
For version 1.5 (2003) you need Acrobat >= 6.0

thanks but does it mean that newer versions of acrobat greater than 6.0 can open documents that were saved as 1.5 in inkscape?

Yes that's what it means. But during process some specificities of your svg can be dropped or degraded (rasterization) if they aren't supported by pdf 1.5 (filters and so on)