It may be necessary to convert CAD annotations into Geodatabase Annotations as part of your daily work. Large CAD drawings usually have a lot of text layers and when they are converted to annotations, due to the number of features in them, performance can be very slow. This makes it very difficult to make changes to the features within the annotation layer. The following article goes over what causes the poor performance and how this can be improved significantly.
The annotations layer in ArcMap has fields like ObjectID, Shape, FeatureID, SymbolID, Bold, Italic, etc. See Knowledge Base article 000008390 for more information on this. From the above mentioned fields, SymbolID is a very important field because this is what defines how the text/annotation is going to be displayed on the map. Each SymbolID value corresponds to a symbol collection, which are listed on the Annotation tab of the annotation feature class's properties in ArcCatalog. The symbol collection defines the font, the size and also its appearance.
If any or all of the following performance issues are encountered, then it is possible that the number of symbol collections in the annotation layer is causing a problem.
If there are many symbols that do not exist under the SymbolID field, but exist in the symbol collections (in ArcCatalog for the same layer) delete all the unused symbols, as described below