With a definite noun, the adjective takes the plural form. Typically the definite article is required as well, but based on the comments above hela and samma are exceptions on this front.
Edit (from the adjective hints):
If the noun is definite, the adjective takes the ending -a in all cases, no matter gender or number. What’s important to note, however, is that whenever a definite noun is used together with an adjective, an article is placed in front of the adjective. This article is den for singular en-words, det for singular ett-words, and de for plural words (note that de is pronounced as ‘dom’).
en stor fisk → den stora fisken ett gult bord → det gula bordet snälla hundar → de snälla hundarna
I guess my question, which is not exclusively related to this question, is whether hela is one of those words that, when plura, can take on a new meaning (to the english speaker, at least) like någon, något, några, or annan, annat, andra. Like, in the Swedish version of "Part of Your World", is "Hela Min Värld", but I don't understand why it's "hela" and not "hel" (or if it is hela, why it's not "Min Hela" instead. So I guess my question is just more related to that one use of the word.
Hela is defenite, and follows definite of rapporten. One can say "jag läser hela rapporten" or "jag läser en hel rapport" (I am reading a whole report).
To specify that it is your report, it is "jag läser hela min rapport" (note the word order).
You kind of could say "jag läser min hela rapport" or "jag läser den hela rapporten", but then "hela" means "not broken" (with emphasis) instead of "entire", which don't really work for a report.