If you add the puff of air after /p/ only at the start of a word immediately before a stressed vowel, nobody will notice its absence anywhere else.
This is a question about what phoneticians call aspirate consonants—stop consonants whose release is accompanied by a distinct puff of air.
In IPA phonetic transcription, which represents the actual sounds produced, aspiration is notated with a superscript ‘h’, thus: [ph].
But in English, the contrast between aspirate and nonaspirate consonants is not phonemic, it does not serve to distinguish different words. What determines aspiration is the phonetic context, the sounds which come immediately before and after a consonant. Native speakers are not even aware of the difference unless they have studied phonetics, as linguists or actors or singers. (But they are aware when a non-native speaker employs aspiration differently from the English norm, if only to think "He talks funny".)
Consequently, aspiration is not marked in the spelling of an English word, because it isn't necessary. (Doubling a consonant tells you about the pronunciation of the previous vowel, not the pronunciation of the consonant.) Even the pronunciation guides you find in dictionaries will not tell you whether a consonant is aspirate or nonaspirate, because these guides are phonemic rather than phonetic: they are concerned to tell native speakers how words are pronounced relative to other English words. The actual phonetic sounds representing each phoneme vary greatly from individual to individual and from dialect to dialect. (Note that the IPA pronunciations which Mari-Lou A provides are phonemic, as may be seen from their enclosure in slashes // rather than the brackets  employed for phonetic representations.)
Speaking generally, in English only the voiceless stops /p/, /t/, /k/ are regularly aspirated, and only in syllable-initial position immediately before a stressed vowel. They are not aspirated after /s/, and they are aspirated only lightly, if at all, before 'liquid' consonants and glides (/l/, /r/, /j/, /w/) and before vowels in in unstressed syllables—this is the phenomenon you observe in apple. The degree of aspiration varies from dialect to dialect.