In French, you never pronounce the “d” at the end of the stem.

“Moreover, do all -re verbs have a d which ends the stem?”
No, it happens when the verb ends with -dre. A simple example of that is the verb “faire”. It ends with -re, but the correct conjugated form is “fais” and not “faids”.

The verb forms comprends, perds, vends are never pronounced with /d/.

I realize you didn’t ask about the third-person forms, but comprend, perd, vend are never pronounced with /d/ either. They have /t/ in certain contexts, e.g. when suffixed with an inverted subject pronoun as in comprend-il, comprend-elle: orthographically, this is considered liaison, but from a phonetic standpoint, it’s indistinguishable from the “euphonic” consonant that shows up after third-person verbs of any conjugation (e.g. “aime-t-il”). The third-person plural verbs spelled with “-dent” are pronounced with /d/; e.g. vendent /vɑ̃d/. (These third-person plural forms are also pronounced with /t/, after the /d/, in appropriate contexts: e.g. vendent-elle /vɑ̃dtɛl/; historically, a schwa was present between these consonants, but I don’t think it’s necessary or even preferable to pronounce schwa in this context in modern Parisian-accent pronunciation. I’m not entirely certain about this, though.) As Karen Jo mentioned, the verb prendre has a special conjugation and its third-person plural form is prennent, which is pronounced as /pʁɛn/, without a /d/.

Principles that I think hold (I’m not entirely certain of my understanding, so be careful with these):

• third-person plural -ent always behaves exactly like -e in terms of how it affects the pronunciation of a verb form: it indicates that preceding consonant letters are pronounced, it can sometimes correspond to the vowel sound /ə/ in certain contexts, and it indicates that when liaison is made after the verb form, the liaison consonant is /t/.

• I can’t think of any finite verb forms in French that are not spelled with silent -e, -es, or -ent and that are pronounced (outside of liaison contexts) ending with any consonant sound, except for /ʁ/. Verbs spelled with -rs, -rt are pronounced with /ʁ/ (e.g. je dors, je sors, je sers) but as far as I know, any consonant letter other than “r” that can show up in this context will be silent. Also, these verb forms do drop a consonant that is present after the “r” in the pronunciation and spelling of other forms of the word: the third-person-plural forms are dorment, sortent, and servent.

More generally, there are a number of -re verbs that end in something other than -dre in the infinitive. The -dre verbs that conjugate like vendre are usually taught relatively early on because a number of them follow a fairly easy/regular pattern. (However, there are “irregular” verbs with infinitives in -dre; aside from the example of prendre, already mentioned, there are verbs like coudre, with the third-person plural cousent /kuz/.)

The conjugation of other verbs ending in -re are even less predictable from the perspective of a learner, although not without patterns. The plural forms, including the third-person plural, are often pronounced with a consonant that is not present in the pronunciation of the singular forms, although it may or may not be present in their spelling.

E.g. the verb vaincre is conjugated in the singular as je vaincs, tu vaincs, il/elle vainc; these forms are all pronounced /vɛ̃/, unlike the third-person plural form ils/elles vainquent which is pronounced /vɛ̃k/ (the orthographic third-person-plural suffix -ent can be seen as an indicator that the consonant /k/ is pronounced in this form of the word). The verb rompre is conjugated in the singular as je romps, tu romps, il rompt; these are all pronounced /ʁɔ̃/, unlike the third-person plural form ils/elles rompent which is pronounced /ʁɔ̃p/.

The CNRTL online dictionary lists the pronunciation of all forms of words, and although it is more conservative than a typical learner’s accent in certain ways (e.g. it marks all “mute e”s as @, its symbol for schwa, regardless of context) I have found it to be helpful when I want to verify information like whether a consonant letter is pronounced or silent.