A .BMK file is typically a bookmark/marker file that stores jump-back locations like pages, timestamps, or saved items, but because `.bmk` isn’t a universal standard, each program uses its own format, meaning a BMK might hold labels, titles, page numbers, timestamps, file paths, IDs, or map/CAD coordinates; some are text-based and show readable URLs or titles in Notepad, while others are binary and look like gibberish, being used for things like PDF/eBook bookmarks, media time markers, CAD/map views, or resume points, and the best way to identify yours is checking where it came from and whether its contents open cleanly in a text editor.

To figure out what a .BMK file is, you must determine which app created it and whether it’s readable text or app-specific binary, so inspect the folder it’s in—program directories, AppData, project folders, or files next to PDFs/videos often reveal its purpose—check Properties for clues like “Opens with,” then try viewing it in Notepad to see if it contains readable entries (titles, page refs, timestamps, or structured data), which means it’s a text-based bookmark, while random symbols imply a binary format meant for the original program, and similarly named nearby files often reveal what document or media the BMK links to.

A .BMK file is used by various apps in incompatible ways which means the only way to know what type you have is to find the program that made it; the strongest clues come from the folder it’s in, Windows’ association, and whether Notepad reveals readable items like page numbers, paths, or labeled markers—gibberish means it’s binary and must be used through its native application.

Once you know the .BMK type, you can immediately decide how to handle it, because text-based BMKs open best in Notepad++, where you can read titles, pages, timestamps, and references before converting them into `.txt`, `.csv`, or URL-based bookmark lists, whereas binary BMKs must be processed inside the original software using features like Import Bookmarks or Restore Session to export into standard formats, and if the source remains unknown, examining its folder context and any readable strings usually reveals the application and proper export path.

A “bookmark file” is essentially a pointer file that keeps track of where an app should jump back to, storing labels you added along with targets like pages, chapter IDs, timestamps, scroll offsets, or coordinates, allowing the software to restore your saved spots whenever the original content opens, whether as bookmarks, markers, or resume points, and because it only stores references—not the data—it often won’t work without the original file it depends on.