If you are designing a poster in PowerPoint you may find it helpful to check the size of your poster by clicking on File>Page Setup.
Please keep in mind that sometimes (rarely) Greek letters and other symbols created on one machine (or version of PowerPoint) are transformed into wingdings and other strange things on another machine, so please make a .pdf copy as a backup.
Please do not use Word, Visio, Pages or Publisher to create your poster as most places do not recognize those formats.
Most poster printing facilities use either PowerPoint or .pdf files as the routine file formats.
For other formats, please check with the printing service you've chosen for compatability.