If there is an answer give it if not just ingnore the post.

My question is regarding страдательные причастия прошедшего времени. For example of the verb прочитать the причастиe is прочитанный

My limited understanding enables me to understand the following things:
1. The 85% of Russians when they are asked about what part of the speech is прочитанный they will answer adjective.
2. The страдательные причастия прошедшего времени are used as adjectives.
3. They have a краткая форма which is most of the times used.
4. In most of the cases they proceed the noun and this is mainly the reason why so many people believe that they are adjectives.
5. The majority of verbs do not have a страдательные причастия прошедшего времени

Some structural issues:
1. Страдательные причастия прошедшего времени are composed from verbs. In order to be formed the following endings are used:
-енный
-атый
-ённый
-анный
2. In some cases the ударение is transfered (increased)

Question: Is there a rule what ending to use when we form them (-енный -атый -ённый -анный )?

Possible answer: Don't bother! You should have to memorize all them. Most of the times when the verb ends in -ать and its First Conjugation Verb you use the ending -анный. In all other cases is just lottery.