Your 50th Birthday Invitations should be written in fine designed invitation cards. This type of birthday invitation is normally written in very friendly tone if most of the invitees are your friends and relatives. However, change the salutation to formal mode when you are intending to invite people from your professional circle. You may also see birthday samples.
In any situation, the body of the Birthday Invitation should be short but detailed. These are available in supported file formats like word, pdf, and psd etc. After applying proper salutation, you need to mention the host of the party, date, time and venue in details. If needed also add nearest landmark and how to reach at the Birthday Party venue if the party is organized in some other place.