Is the repitition of 'can' in this sentence a use of poor grammar?

Is the repetition of 'can' a use of bad grammar?

"[...] certain files can be reduced in size and can still retain all crucial information [...]"

Should it simply be ""[...] certain files can be reduced in size and still retain all crucial information [...]"?

Thank you for your help.

It's certainly not ungrammatical.

certain files can be reduced in size and can still retain all crucial information

Removing the second "can" could make the sentence slightly ambiguous. Consider the following sentence:

Cats can be a source of great comfort and can sit on your lap.

The comfort and lap sitting are not connected.

Cats can be a source of great comfort and sit on your lap.

The comfort and lap sitting are probably connected although it's ambiguous. It could mean either:

Cats can [be a source of great comfort and sit on your lap].

or

Cats can [be a source of great comfort] and [sit on your lap].

In your particular context (file compression) the two go together (reduction in size and retaining information), so there is little room for ambiguity.