I have been davening from my ipad using a pdf copy of a siddur I downloaded. However, I wanted to know if this is a suitable alternative for those times when the use of electronic devices is permissible. Does this present any halacha violation?
I found a discussion of possible problems, the writer seems not to like the idea, though doesn't rule it out completely.
Issues that are addressed there (my comments in parentheses):
To sum it up, I personally don't see a problem. I would add one should have a regular siddur for use on Shabbat and Chagim, because if he gets used to relying on the iPad he can get stuck on those occasions.