I think this task was already done. You can see it on the ChangeLog file,
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* doc/gnupdf.texi: updated API to conform the "const" convention.
* src/base/pdf-alloc.c: updated API to conform the "const" convention.
* src/base/pdf-alloc.h: updated API to conform the "const" convention.
* src/base/pdf-error.c: updated API to conform the "const" convention.
* src/base/pdf-error.h: updated API to conform the "const" convention.
* src/base/pdf-hash.c: updated API to conform the "const" convention.
* src/base/pdf-hash.h: updated API to conform the "const" convention.
* src/base/pdf-list.h: updated API to conform the "const" convention.
* src/base/pdf-text.c: updated API to conform the "const" convention.
* src/base/pdf-text.h: updated API to conform the "const" convention.
* src/base/pdf-types.c: updated API to conform the "const" convention.
* src/base/pdf-types.h: updated API to conform the "const" convention.
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Though, I didn't know there was an open task for it, sorry.
-gerel
